Elastomeric articles, compositions, and methods for their production

ABSTRACT

This application relates to synthetic elastomeric articles, such as gloves, comprising the cured product of a synthetic latex composition, the synthetic latex composition comprising a synthetic carboxylated polymer and a cross-linking composition, the cross-linking composition comprising an aqueous solution of a negatively charged multivalent metal complex ion having a pH of at least 9.0. Also described are compositions for forming the articles, and methods for making the articles, based on the use of the described cross-linking composition. The articles, compositions and methods contain a second cross-linking agent comprising either (a) sulphur and a sulphur donor, (b) a multivalent metal oxide or ionic cross-linking agent, (c) sulphur, a sulphur donor and an ionic cross-linking agent, or (d) sulphur donor.

FIELD

The present invention relates to elastomeric articles, compositions, andmethods for their production. The articles may be in the form of films,gloves, condoms or otherwise. The compositions are suitable for formingarticles through a dipping processes.

BACKGROUND

Important properties in the formation of many elastomeric articles areelasticity, the maintenance of elastic properties on stretching, andsoftness. In the case of elastomeric gloves, and particularly thin filmgloves, these properties are very important and impact on the comfort ofthe gloves to persons wearing them.

When a thin film glove is worn for barrier protection by a person, thegloves can become uncomfortable after a short period of time, due tofatigue associated with the resistance of the glove, which is in turn aresult of an intrinsic character known as “lesser elasticity”. Thisproperty is measured in terms of its modulus (which may be measured at500%, or preferably at 300%). It is desirable for a glove for use insuch applications to have a lower modulus.

In relation to elasticity, it is often desirable in certain applicationsfor the elastomeric article to have high elasticity properties, asindicated by a high capacity to be stretched, or elongated, beforebreakage. This is measured by a test that determines elongation, or morespecifically, elongation at break.

It is difficult to achieve a balance of a low modulus, combined withhigh elongation at break, as well as desirable “feel” or touchproperties, particularly without the additional potential problems thatmay arise through the incorporation of potential allergens. Gloves thatare made from natural (polyisoprene) rubber have favourable feel andcomfort properties, and can be made with a good balance betweenfavourable modulus and elongation properties. However, natural(polyisoprene) rubber is associated with a potential allergen thatcauses Type I allergy. Accordingly, articles formed from syntheticelastomer alternatives having the same or improved properties comparedto natural rubber are desired.

The current trend is to use nitrile rubber, (synthetic) polyisoprenerubber, polychloroprene rubber, styrene butadiene rubber, butyl rubberand/or vinyl in the production of elastomeric articles, such as gloves.These polymers are traditionally cross-linked with finely milled (solid)zinc oxide and/or sulphur cross-linking agents. Some of these materialsdo not provide the favourable feel and comfort of natural polyisoprenerubber. Others of the known cross-linked synthetic polymers, whilehaving reasonable feel and comfort properties, are very expensive,making them unsuitable for the production of low cost, disposableelastomeric articles, such as gloves, condoms and the like. Althoughreducing the thickness (weight) of such articles made from the moreexpensive elastomeric polymers has been considered, reduced thicknessproducts are at an increased risk of containing defects. The defects maybe in the form of holes due to poor film formation at such finethicknesses and/or lower endurance properties compared to the propertiesrequired by the consumer.

Elastomeric compositions have potential application in many fields, andcan be used in the production of elastomeric articles other than thinfilm gloves (including medical gloves, surgical gloves, examinationgloves) and condoms. Other examples of elastomeric articles includethose for medical applications such as catheters, tubing, protectivecoverings, balloons for catheters and the like, and those for use innon-medical applications, such as industrial gloves, laboratory gloves,household gloves, gardening gloves, electrical gloves, irradiationgloves, finger cots, weather balloons, clean room gloves for electronicindustries, gloves for food contact and food processing and biotechnicalapplication and the like. By expanding the range of potential newelastomeric film compositions that are available, particularly low costelastomeric article compositions, the compositions can be used in theproduction of a wider range of these articles, and new applications forthe compositions may be developed.

In some applications and embodiments, it may also be desirable toprovide new elastomeric articles, formed from new compositions, that canbe produced at reduced cost. The areas for potential cost reduction maybe the cost of the input components or reagents, the physical processingcosts (including energy costs for performing certain production steps),and so forth.

In some applications and embodiments it may be desirable to avoid theuse of reagents that have, or may have, an adverse impact on theenvironment.

It is an object of the present invention to provide new elastomericarticles, and compositions for the production of such articles, thatprovide one or more of the desired features described above.

SUMMARY

According to the present invention, there is provided a syntheticelastomeric article comprising the cured product of a synthetic latexcomposition, the synthetic latex composition comprising a syntheticcarboxylated polymer and a cross-linking composition, the cross-linkingcomposition comprising an aqueous solution of a negatively chargedmultivalent metal complex ion having a pH of at least 9.0.

According to the present invention, there is also provided anelastomeric article-forming composition (also referred to as a“synthetic latex composition” or “latex composition” for short)comprising:

-   -   a synthetic carboxylated polymer, and    -   a cross-linking composition, the cross-linking composition        comprising an aqueous solution of a negatively-charged        multivalent metal complex ion having a pH of at least 9.0.

According to the present invention there is also provided a method ofmanufacturing a synthetic elastomeric article comprising:

-   -   adding a cross-linking composition comprising an aqueous        solution of a negatively-charged multivalent metal complex ion        having a pH of at least 9.0 to an aqueous suspension of a        synthetic carboxylated polymer having a pH of at least 9.0 to        produce a synthetic latex composition;    -   forming the synthetic latex composition into the shape of the        synthetic elastomeric article; and    -   curing the synthetic latex composition to form the synthetic        elastomeric article.

In contrast to prior art articles and compositions, the articles andcompositions of the present invention involve the use of a solubilisedform of a multivalent metal, in a complex ion form which has an overallnegative charge, at a pH of at least 9.0. The multivalent metal thenforms cross-links between carboxyl groups of the carboxylated polymerduring the cross-linking or curing stage in the manufacture of thearticle. Through the exercise of considerable skill and effort, theinventors were able to achieve solubilisation of the multivalent metaland maintenance of the multivalent metal in solution without (or withoutsignificant) precipitation of insoluble forms of the multivalent metalduring the time of adding the cross-linking agent to the suspension ofsynthetic carboxylated polymer in water. Combining of the cross-linkingagent with the aqueous suspension of synthetic carboxylated polymer wasconducted very carefully to avoid disruption to the suspension of thepolymer in water—that is, without disruption of the emulsion. One keyfactor in enabling this to be achieved involves controlling the pH ofthe respective cross-linking composition and the aqueous suspension ofthe synthetic carboxylated polymer. Other factors that assist inachieving this result are set out in the detailed description below.

In key embodiments of the present invention, the synthetic latexcomposition further comprises a second cross-linking agent comprisingeither (a) sulphur and a sulphur donor, (b) a multivalent metal oxide orionic cross-linking agent, (c) sulphur, a sulphur donor and an ioniccross-linking agent, or (d) sulphur donor.

Thus, in one aspect, there is provided a synthetic elastomeric articlecomprising the cured product of a synthetic latex composition, thesynthetic latex composition comprising a synthetic carboxylated polymerand a cross-linking composition, the cross-linking compositioncomprising an aqueous solution of a negatively charged multivalent metalcomplex ion having a pH of at least 9.0, the synthetic latex compositionfurther comprising a second cross-linking agent comprising either (a)sulphur and a sulphur donor, (b) a multivalent metal oxide or ioniccross-linking agent, (c) sulphur, a sulphur donor and an ioniccross-linking agent, or (d) sulphur donor.

In another aspect there is provided an elastomeric article-formingcomposition comprising:

-   -   a synthetic carboxylated polymer,    -   a cross-linking composition, the cross-linking composition        comprising an aqueous solution of a negatively-charged        multivalent metal complex ion having a pH of at least 9.0, and    -   a second cross-linking agent comprising either (a) sulphur and a        sulphur donor, (b) a multivalent metal oxide or ionic        cross-linking agent, (c) sulphur, a sulphur donor and an ionic        cross-linking agent, or (d) sulphur donor.

In a further aspect there is provided a method of manufacturing asynthetic elastomeric article comprising:

-   -   adding (i) a cross-linking composition comprising an aqueous        solution of a negatively-charged multivalent metal complex ion        having a pH of at least 9.0 and (ii) a second cross-linking        agent comprising either: (a) sulphur and a sulphur donor, (b) a        multivalent metal oxide or ionic cross-linking agent, (c)        sulphur, a sulphur donor and an ionic cross-linking agent,        or (d) sulphur donor, to an aqueous suspension of a synthetic        carboxylated polymer having a pH of at least 9.0 to produce a        synthetic latex composition;    -   forming the synthetic latex composition into the shape of the        synthetic elastomeric article; and    -   curing the synthetic latex composition to form the synthetic        elastomeric article.

The use of these selected second cross-linking agent combinations (orsole secondary agents) provides for particularly good properties incombination with the negatively-charged multivalent metal complex ionsof the primary cross-linking composition. The use of these agents incombination with the multivalent metal ions allows for low reagentutilisation in the production of gloves, and also produces gloves havingexcellent properties, as demonstrated in various examples in thisspecification.

The synthetic carboxylated polymer typically comprises syntheticcarboxylated polymer particles. Reaction of the solubilised multivalentmetal with the carboxylated polymer particles is understood to result ina cured product in which the synthetic carboxylated polymer particlesare bonded to each other through intra-polymer particle multivalentmetal cross-links and inter-polymer particle multivalent metalcross-links, in which the intra-polymer particle and inter-polymerparticle multivalent metal cross-links are uniformly distributedthroughout the cured product.

Thus, according to a further embodiment of the invention, there isprovided a synthetic elastomeric article comprising cured syntheticcarboxylated polymer particles bonded to each other throughintra-polymer particle multivalent metal cross-links and inter-polymerparticle multivalent metal cross-links, in which the intra-polymerparticle and inter-polymer particle multivalent metal cross-links areuniformly distributed throughout the cured product.

According to another embodiment of the invention, there is provided across-linking composition comprising an aqueous solution of anegatively-charged multivalent metal complex ion having a pH of at least9.0. According to preferred embodiments, this cross-linking compositionfurther comprises a mechanical stabiliser and/or a surfactant.

DETAILED DESCRIPTION

The synthetic elastomeric article, composition and methods ofmanufacture are described in further detail in this section.

Cross-Linking Composition

The present inventors have developed a new form of cross-linking agentcomposition, which is based on an aqueous solution of anegatively-charged multivalent metal complex ion having a pH of at least9.0.

The inventors developed this invention using the example of sodiumaluminate in the production of negatively-charged multivalent metalcomplex ions, in which the multivalent metal is aluminium. However, asdescribed in detail below, embodiments of the invention are applicableto a wider range of multivalent metals, and sources of the metals, inthe production of the cross-linking composition. In this introductoryportion of the detailed description, reference is made to the example ofnegatively-charged aluminium complex ions, and sodium aluminate as asource for those ions, to illustrate the invention and explain theadvantages that are obtained over prior art compositions. However, thisshould be read in this context and should not be understood as confiningthe scope of the invention.

In the prior art, it is common to use zinc oxide as an ioniccross-linking agent in the production of elastomeric articles such asgloves. Zinc oxide, and other oxides of the multivalent metals, aretypically insoluble in water. Zinc oxide is incorporated into latexcompositions used in the formation of elastomeric gloves in solid form.Zinc oxide does not have significant solubility in water. In high pHenvironments, there may be some diffusion of the solid zinc oxide intosolution, but this process is slow and incomplete. The zinc oxide istypically finely milled, to provide a high surface area to the reagentto maximise availability of the zinc oxide to produce ionic zinccross-links with the polymer being cross-linked, to form a cross-linkedor cured product. The milling step requires energy input to achieve. Inaddition, there is incomplete usage of the zinc, and thus the amountadded (measured in terms of phr—“per hundred parts rubber”) must be highenough to allow for the incomplete reaction of the reagent. Zinc alsofinds its way into the air or wastewater during manufacturing, use orrecycling of products containing zinc. This can have an adverseenvironmental impact, and it is becoming more important to reduce orremove zinc from products.

Another problem with conventional zinc oxide is associated with themanner in which solid zinc oxide forms cross-links within the finalproduct. As explained above, the synthetic carboxylated polymer is inthe form of a particulate suspension or emulsion in water. When usingsolid zinc oxide as the cross-linking agent, the cross-links tend to beconcentrated around the particles, and the cross-links are predominantlyinter-particle cross links. In this regard, reference is made toWO09/134702, which includes spectral information showing the typicalpattern of zinc in the product when solid zinc oxide is used as an ioniccross-linking agent. The zinc is concentrated around the particles, anddecorates the particles. Soluble forms of sulphur in that case areallowed to penetrate into the particles, and form inter-particlecross-links. There is little penetration of the zinc into the polymerparticles, if any, in view of the lack of any significant solubility ofzinc in typical latex emulsions under typical conditions.

In the art of the invention, it is uncommon in practice to modifyproducts to use ionic cross-linking agents other than the well-known andwell understood zinc oxide, and other solid multivalent metal oxides.Even if they had been considered from a theoretical perspective, it isthe present inventors' experience that it is extremely difficult inpractice to put this idea into effect.

Nevertheless, after considerable effort, the present inventors were ableto produce a solubilised form of multivalent metal cross-linking agent,and were able to combine this with an aqueous suspension of syntheticcarboxylated polymer, and were able to produce a synthetic latexcomposition that is very effective in creating elastomeric articleshaving excellent properties. The inventors found that it is notsufficient to add a solid form of the multivalent metal (such as zincoxide) to the synthetic latex composition, and to seek to increase thepH and take additional steps to attempt to solubilise the multivalentmetal. As an example, taking solid zinc oxide or another solid oxide andadding this to an aqueous suspension of synthetic polymer (carboxylateor otherwise) and then attempting to solubilise the oxide in situthrough pH adjustment or heating is not effective. Instead, a stableaqueous solution of negatively charged multivalent metal complex ionsmust be prepared as a preliminary step, with optional stabiliser and/orsurfactant addition, and with pH control, and this composition is to beadded in a controlled manner to the aqueous suspension of syntheticpolymer which is also subjected to pH control. The streams are then tobe carefully combined while avoiding disruption of the emulsion, latexlump formation through micro-coagulation, precipitation or othersettling of the components from the composition.

In some embodiments it is additionally important to control otherfactors in the composition, article or process. The features of suchembodiments are described in further detail below.

Multivalent Metal

The term “multivalent metal” refers to a metal having a valency of twoor more. The expression “divalent or higher valency” may be usedinterchangeably with “multivalent”. In some embodiments, the multivalentmetal is a trivalent metal.

Whilst aluminium is the preferred multivalent metal, in someembodiments, the multivalent metal of the negatively-charged multivalentmetal complex ion can be another of the class of amphoteric metals. Theamphoteric metals are those metals that form amphoteric substances fromtheir oxides and/or hydroxides. This class includes aluminium,beryllium, chromium, zinc, copper, iron, cobalt, lead, tin, bismuth,gallium, indium, scandium, titanium, zirconium, vanadium, silver, gold,germanium, antimony and tellurium. The multivalent metal of thenegatively-charged multivalent metal complex ion is preferably selectedfrom the group consisting of aluminium, beryllium, chromium, iron,cobalt, copper, zinc, lead, tin and bismuth. The multivalent metal maybe selected from aluminium and beryllium. Trivalent (or higher valency)metals are preferred, and aluminium is most preferred in selectedembodiments.

To produce the cross-linking composition, initially a solution is formedby dissolving a source of the multivalent metal in water. This may beachieved with heating and the optional addition of an alkali and/or amechanical stabiliser and/or a surfactant. In some notable embodiments,it is a feature that a mechanical stabiliser and/or surfactant isincluded in the cross-linking composition.

Regarding the source of the multivalent metal, a suitable source needsto be chosen that is capable of yielding a solution of negativelycharged multivalent metal complex ions. This may require pH adjustmentof the solution to achieve solubilisation. Suitable sources included (a)a multimetal oxide of the multivalent metal, (b) a hydroxide of themultivalent metal or (c) a salt of the multivalent metal.

Regarding the first class, being the multimetal oxides of themultivalent metal, this term refers to an oxide of the multivalent metalwith another one or more different metal species. Such multimetal oxidesof the multivalent metal may be referred to as “multimetal oxides” inshort. Such materials may also be viewed as a mixed metal oxides. Wherethere are two metals, the oxide may be described as a double metaloxide. The second metal species may be, for example, an alkali metal,such as sodium or potassium. In the case of aluminium as the multivalentmetal, the second metal species is preferably sodium or potassium, alsoreferred to as sodium aluminate and potassium aluminate. Thus, in oneexample, the multimetal oxide of the multivalent metal may be an alkalimetal-multivalent metal oxide.

Regarding the second class, being hydroxides of the multivalent metal,these may simply be referred to as metal hydroxides. In practice, toachieve the production of the negatively charged multivalent metalcomplex ion, a second hydroxide (such as an alkali metal hydroxide) isrequired, with a consequent increase in the pH required forsolubilisation of the multivalent metal hydroxide. The hydroxides of themultivalent metals may in some cases be viewed as the hydratedmultivalent metal oxides, and the source of the multivalent metalhydroxide may in practice be a multivalent metal oxide (particularly amixed metal oxide). In solution, there may be a mixture of differenthydroxides of the multivalent metal, in different complex ion forms.This is elaborated on in further detail below using the example ofaluminium.

Regarding the third class, being the salts of the multivalent metals,the salt will typically require considerable alkali addition (such asalkali metal hydroxide) to achieve solubilisation of the multivalentmetal and production of the negatively charged multivalent metal complexions. Solutions of multivalent metal salts are not typically alkaline,and it may be necessary to add considerable alkali to raise the pH to atleast 9.0. It is important in such cases for the negatively chargedmultivalent metal complex ions to be produced on raising the pH, withoutsignificant precipitation of an insoluble salt. Examples of saltsinclude alum (potassium alum, or potassium aluminium sulphate), polyaluminium chloride (also referred to as AlCl₃), and poly ferricsulphate. The pH of 10% solutions of these salts are 2.83, 3.27 and 1.7,respectively, so considerable alkali (in the form of alkali hydroxide)is required to raise the pH to at least 9.0 and to form the negativelycharged multivalent metal complex ions.

The first two classes are preferred, thus it is preferred that thecross-linking composition comprises a solution of a multimetal oxide ofthe multivalent metal or a solution of a multivalent metal hydroxide.

Of the range of multivalent metals, the source of multivalent metal mayonly be available from one or two of the above groups of potentialsources ((a), (b) and (c)). Thus, in the case of iron, iron hydroxide isnot a suitable source for the preparation of solubilised negativelycharged iron complex ions due to its lack of solubility. In the case ofaluminium as the multivalent metal, sources from each of the possiblegroups ((a), (b) and (c)) are available.

As indicated above, in some embodiments, the cross-linking compositioncomprises a solution of sodium aluminate, producing negatively-chargedaluminium complex ions. The primary ions formed are thetetrahydroxoaluminate (III) ions—being a complex of a central aluminiumatom with co-ordinating hydroxo ligands. Aqua (water) ligands may alsoform part of the complex ions. Other ions in the solution will includethe aluminium and alkali metal (e.g. Na). The range of negativelycharged aluminium complex ions produced on solubilising sodium aluminateis reported in the literature. At varying pH levels, the equilibriumbetween the various ions will differ. The key to maintaining solublealuminium complex ions is to maintain the pH above 9.0, as below 9.0insoluble Al(OH)₃ is formed, which precipitates out of solution. Withother multivalent metals, the pH must be such that the solublenegatively-charged complex ions of the multivalent metal are formed, andan insoluble precipitate is minimised or avoided. In this regard,preferably not more than 20%, more preferably not more than 15%, 10%, 5%or less than 2% of the multivalent metal is in the form of an insolubleprecipitate (precipitated out of solution). These percentages applyregardless of the source used, and regardless of the identity of themultivalent metal that is solubilised to form the negatively-chargedmultivalent metal complex ion.

Sodium aluminate is a basic inorganic chemical used in water andeffluent treatment industries. These salts are used as coagulants tosettle fine particulate materials in water streams, such asbicarbonates. This is available at low cost, which allows for reducedcost of production of the new elastomeric articles of the presentinvention, which may lead to the development of new applications for theelastomers. Being a water treatment chemical, sodium aluminate is alsoconsidered to be safe for use, and safe for food-contact applications.

Other advantages associated with the use of sodium aluminate, or othercross-linking agent sources as described herein, are as follows:

-   -   There is no cost associated with milling (in contrast to solid        zinc oxide and other prior art solid cross-linking agents)    -   It is possible to eliminate zinc usage, if so desired. In such        embodiments, the cross-linking composition is free of zinc, or        substantially free of zinc. In some embodiments, the latex        composition is also free of zinc, or substantially free of zinc.        Eliminating zinc will avoid excess liberation of zinc to the        environment. In some countries such as Japan, there are limits        on the detectable level of zinc in components involved in food        handling. (Note that it is nevertheless an option in some        embodiments to use a second cross-linker which is based on a        different multivalent metal oxide compared to the solubilised        one, such as zinc oxide, as described in further detail below.)    -   Aluminium has a low atomic weight of 27 and a specific gravity        of 2.7. Compared to conventional cross-linkers, such as zinc        (atomic weight 65 and specific gravity 7.14) this is low. Per        molecule that requires cross-linking, less weight of        aluminium-based reagent is required. This allows for further        cost reduction in the manufacture of elastomeric articles using        aluminium (or similar) ionic cross-linking agent, particularly        when little or no zinc cross-linking agent is added.    -   Aluminium has a valency of 3, allowing for 3-links per molecule.        In contrast, zinc, with a valency of 2, allows for 2-links per        molecule. This allows for a theoretical 50% in the cross-linking        ability of aluminium compared to zinc, even leaving aside the        solubilising effect (compared to solid zinc oxide). This is        another factor that allows for reduction in the mass of ionic        cross-linking agent to be used.    -   Aluminium in this form is not subject to purity concerns,        allowing it to be used in a range of applications. Aluminium is        abundant, and safe for food applications (as reflected by the        use of aluminium foil food packaging.)    -   In view of the effectiveness of the cross-linking with the        solubilised multivalent metal, it is possible to produce        products with lower, or no, sulphur, and/or lower, or no,        sulphur donor materials. This also applies to embodiments using        multivalent metals other than just aluminium. Whilst it is        possible to produce products with lower, or no, sulphur and/or        lower, or no, sulphur donors, in some embodiments, excellent        products can be produced containing either (a) sulphur and a        sulphur donor, (b) a multivalent metal oxide or ionic        cross-linking agent, (c) sulphur, a sulphur donor and an ionic        cross-linking agent, or (d) sulphur donor, as the second        cross-linking agent. In such embodiments it is possible to        produce excellent products suitable for commercial production        containing low levels of the solubilised multivalent metal        oxide, hydroxide or salt, with low levels of the sulphur and        sulphur donor (alone or with an ionic cross-linking agent), or        sulphur donor alone.    -   If the option is taken to form the product without sulphur and        sulphur donor materials, which is possible in view of the        cross-linking performance of the composition (particularly when        a second cross-linking agent that is an organic cross-linking        agent other than sulphur or a sulphur donor is used), the        product is free of Type IV allergens. Further, as natural rubber        is not used (containing proteins and other potential Type I        allergens), the products are also free of type I allergens. This        also applies to embodiments using multivalent metals other than        just aluminium.    -   Homogeneity is improved, as a consequence of lightness and the        ionic nature of the negatively-charged complex. Intra-particle        cross-links can be formed at a similar distribution to the        inter-particle cross-links. Homogeneity can be further maximised        through the use of stabilising agents, as described below. This        also applies to embodiments using multivalent metals other than        just aluminium.    -   Loss due to milling wastage is avoided. Loss due to settling        during storage or in the dipping tank is avoided. This also        applies to embodiments using multivalent metals other than just        aluminium, since in each case a solubilised form of multivalent        metal is used.    -   The multivalent metal, in aqueous ionic form, can instantly        react with the carboxylic groups on the polymer. This can be        achieved at room temperature, thus leading to potential cost        savings associated with avoided heating. Whilst the        cross-linking can be conducted at lower temperature (e.g.        <40° C. or <30° C.), higher temperatures may still be used to        achieve cross-linking of second cross-linking agent(s), if        present. This also applies to embodiments using multivalent        metals other than just aluminium.    -   Dipped articles produced using the cross-linking composition        have high tensile value at break (greater than 1000 psi (6.9        MPa), or even up to 6000 psi) and elongation to break (greater        than 400%, typically greater than 650%, or greater than 700%, or        as high as 900% or more). Lower modulus at 300% and at 500% are        also obtained. Modulus values at 500% (aged and unaged) can be        so low as to be below 7.0 MPa, or below 6.9, 6.8, 6.7, 6.6, 6.5,        6.4, 6.3, 6.2, 6.1, 6.0 or even lower. This applies in        particular to films having a thickness of less than 2.0 mm (i.e.        an average thickness across three test points, for a sample size        of at least 10 articles). This also applies to even thinner        films (less than 1.9 mm, less than 1.8 mm films, etc). The        examples demonstrate that the physical properties are directly        proportional to the ppm level of multivalent metal        (corresponding to the amount of multi metal oxide source used in        forming the cross-linking composition). This also applies to        embodiments using multivalent metals other than just aluminium,        although aluminium-based cross-linking agents give particularly        good results. Further, and surprisingly, embodiments using low        levels of aluminium-based solubilised cross-linking agents        provide particularly good results with low input of total        cross-linking agents (in phr).    -   Articles, such as gloves, made using the cross-linking        composition and through the associated method have been found to        possess highly favourable characteristics such as favourable        feel and comfort, and improved softness. The gloves have high        elasticity, as indicated by a high % elongation at break, and/or        a very low modulus at 500% —both aged and unaged, even with low        thickness levels (average 2.0 mm or less). Gloves can be made        from very thin layers of elastomeric film without increasing the        presence of defects such as pin holes, weak spots or other        defects. These improvements may be even better when using the        combination of one or more surfactants, additional cross-linking        agents, and optionally a second polymer which is a carboxylated        or non-carboxylated synthetic polymer. This also applies to        embodiments using multivalent metals other than just aluminium.    -   Gloves made from the product are easy to don. This also applies        to embodiments using multivalent metals other than just        aluminium.

Alkali in Cross-Linking Composition and pH

In embodiments of the invention, the cross-linking composition furthercomprises alkali. This may be added in the form of sodium hydroxide,potassium hydroxide or ammonium hydroxide. Sodium and/or potassiumhydroxide are most typically used. The alkali serves to increase the pHto the level required for solubilisation and/or to chemically stabilisethe solution of negatively charged multivalent metal complex ions.

In some embodiments, a combination of sodium hydroxide and potassiumhydroxide is used. The sodium hydroxide interacts with the aluminium(where this is the multivalent metal) in the formation of complex ions.Potassium hydroxide is more commonly used in latex compositions, and thepresence of potassium hydroxide as one of the alkalis assists inavoiding potential localised coagulation when the cross-linking agent isadded to the aqueous suspension of synthetic carboxylated polymer. Ifsodium hydroxide alone is used as the alkali, there is a risk oflocalised coagulation when the cross-linking agent is added to theaqueous suspension of the polymer, due to the high activation energy ofsodium ions. The relative amount of sodium hydroxide to potassiumhydroxide may be about 3:1 to 1:3. The amount may be about 2:1 (sodiumto potassium) or about 1:1.

The pH of the cross-linking composition is important. The pH must besuch that solubilisation of the multivalent metal is achieved, throughproduction of negatively charged multivalent metal complex ions. It isalso a feature of the method of embodiments of the invention that the pHof the cross-linking composition is “matched” to the pH of the aqueoussuspension of synthetic carboxylated polymer. This is described infurther detail below. In general terms, the pH should be high enough toachieve solubilisation of the multivalent metal. This may be between 9.0and 13.5, such as between 9.0 and 13.0, 9.0 and 12.5, 9.0 and 12,between 9.0 and 11.5, such as between 9.0 and 11.0, 9.2 and 11.0, 9.5and 11.0, 9.5 and 10.5, 9.8 and 10.8, 10.0 and 11.0, or 10.0 and 10.8.When a salt form of the multivalent metal is used, it is preferred touse a higher pH to subdue the acidic properties, so a pH of around10.0-13.0 may be desired, such as between about 11.5 and 12.5, or about12.

In addition to influencing the pH of the cross-linking composition, thealkali has an influence on the stability of the complex ions insolution. Sodium from sodium oxide stabilises the complex ions insolution. Higher amounts of sodium hydroxide allow for greateractivation of the multivalent metal (e.g. aluminium) in the complex, andallows for a reduced amount of multivalent metal source to be used inthe composition.

Mechanical Stabiliser in the Cross-Linking Composition

While it is possible for the cross-linking composition to be preparedwithout any mechanical stabiliser, it is advantageous to include in thecross-linking composition a mechanical stabiliser for mechanically (i.e.structurally) maintaining the negatively-charged multivalent metalcomplex ions in solution. The mechanical stabiliser aids on maintainingthe stability of the solution, by providing structural support aroundthe complex ions to avoid re-precipitation or re-crystallisation. Themechanical stabiliser may be any agent that has this function. Themechanical stabiliser may be a water-miscible or water-soluble organicpolyol, or a water-soluble or water-miscible thickening agent, examplesof which are well known in food or pharmaceutical manufacture. Examplesof such polyols and thickeners include glycerine, sugars and sugaralcohols, maltodextrin, polysaccharide, polyglycerol, polyethyleneglycols, starch, modified starch, and mixtures thereof.

Amounts of Components in the Cross-Linking Composition

The amount of multivalent metal in the latex composition may be anywherebetween 0.01-5 phr across the range of embodiments described herein.Although that is the case, in particular embodiments, the phr amountsused may fall within a narrower range of values. Amounts in “phr” arecommonly used in the art. Phr refers to parts per hundred parts ofrubber (i.e. per hundred parts of the polymer), by weight. In caseswhere reference is made to the amount of multivalent metal (as distinctfrom the source of the metal, such as sodium aluminate), the phr amountrefers to the amount of metal itself, rather than the agent or complexthat it is part of.

Whilst any amount within this range may be used, in particularembodiments a low amount of multivalent metal is incorporated into thecomposition. The amount may be within the range of 0.01-0.5 phr. Inparticular embodiments, the amount of multivalent metal ion is not morethan 0.3 phr, preferably less than 0.3. The amount may be 0.29, 0.28,0.27, 0.26, 0.25, 0.24, 0.23, 0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16,0.15, 0.14, 0.13, 0.12, 0.11 or 0.10 phr. Using low levels of themultivalent metal (and the multivalent metal source in particular) inthe cross-linking composition produces gloves having excellentproperties, with low reagent utilisation, as demonstrated in variousexamples in this specification.

In other embodiments, the amount may be within the broader range of0.01-1.0 phr, including ranges up to 0.9, 0.8, 0.7, 0.6, 0.5 phr. Theamount may in some embodiments be less than 0.4 or 0.3, or 0.25, or 0.2,or 0.15 or 0.1. This contrasts to the typical amount of zinc oxide usedin practice in synthetic polymeric products. (Although prior artdocuments may refer on paper to low levels of ionic cross-linking agent,in practice, films with low solid ionic cross-linking agents do notperform well, and are therefore not commonly manufactured.) The minimumamount may be from 0.02, 0.03, 0.04 or more. The amount used in someembodiments is about 0.05 or about 0.1. Other approximate amounts willbe evident from the range of examples shown in this application.

When a multi metal oxide is used as the source of the multivalent metal,the amount of multi metal oxide in some embodiments may be broadlywithin the range of 0.01-5.0 phr, but in particular embodiments theamount is less than 0.3 phr. The minimum amount may be from 0.01, 0.02,0.03, 0.04, 0.05, 0.1 or more. The amount used in some embodiments is0.15 or about 0.5, but in other embodiments the amount used islower—amounts of about 0.05, 0.08, 0.1, 0.12 or 0.2 are demonstrated inthe examples. The maximum amount may be significantly less than 5.0, andmay be a maximum of (or less than) 4.0, 3.0, 2.5, 2.0, 1.5, 1.0, 0.9,0.8, 0.7, 0.6, 0.5, 0.4, 0.3, 0.29, 0.28, 0.27, 0.26, 0.25, 0.24, 0.23,0.22, 0.21, 0.20, 0.19, 0.18, 0.17, 0.16, or 0.15. Any minimum andmaximum may be combined without limitation. In some embodiments, wherethe degree of carboxylation of the polymer is higher, the amount ofmulti metal oxide used could be at the higher end of the range. Forexample, the amount of multi metal oxide as the source for thecross-linking agent could be within one of the following ranges: 0.15 to5 phr, 1.0 to 5 phr, 2.0 to 4.0 phr, 2.5 to 5 phr or 3.0 to 5.0 phr. Inother embodiments, where the degree of carboxylation is low, or there isa high percentage of other polymers that undergo covalent cross-linking(or are self-crosslinkable), the amount of multi metal oxide as thesource for the cross-linking agent could be lower. Suitable rangesinclude 0.01-1.0, 0.01-0.8, 0.01-0.6, 0.01-0.5, 0.01-0.4, 0.01-0.3 or0.01-0.2. These amounts have been determined using the example of sodiumaluminate as the source. To determine the corresponding phr ranges forthe multivalent metal per se (to allow for a range to be determined forother sources), the phr values in the ranges shown above for thehigh-carboxylated polymer and low-carboxylated polymer cases can bemultiplied by 33%. It is also acceptable to rely on these phr ranges forany of the different sources of multivalent metal oxides, hydroxides orsalts, given the typical relative % amounts of the multivalent metal toother ions in the sources.

Alternatively, one can calculate a particular phr range for a source ofthe multivalent metal that is other than the metal oxide. To calculatethe amount of the source that may be used from the phr ranges providedabove for the multivalent metal, one would multiplying the upper and/orlower limits of the particular range by a factor that reflects the % ofthe multivalent metal in the source. Thus, using the example of alum(containing about 5% aluminium) and the phr range for aluminium of0.01-0.5, the values are multiplied by 20 to give a phr range of 0.2-10phr alum.

Preparation of the Cross-Linking Composition

The cross-linking composition is typically formed by solubilising amultimetal oxide of the multivalent metal, a hydroxide of themultivalent metal or a salt of the multivalent metal in water, andcontrolling the pH to be at least 9.0. Heating may be useful, ornecessary, for solubilisation. In the example of sodium aluminate as themultimetal oxide of the multivalent metal, the composition is typicallyformed by solubilising (or dissolving) sodium aluminate in water withheating.

In some instances, heating can be avoided. However, heating can assistto maximise dissolution. The heating may be to a temperature of at least35° C., at least 40° C., at least 50° C., at least 80° C. or around 95°C. to boiling. Control of the pH is typically achieved through additionof alkali, as described above, to raise the pH to at least 9.0 (to thespecific level set or targeted for the process). The pH mayalternatively be adjusted for pH stabilisation at a target pH level.Control of the pH may otherwise be achieved through the use of amultimetal source that has a high pH. Nevertheless, even if the pH isabove the required level, it is usually necessary to add further alkalito control the pH more precisely, to allow matching of the pH to that ofthe aqueous suspension of the synthetic carboxylated polymer. Further,as described above, having a combination of sodium and potassiumhydroxide provides advantages when the cross-linking composition and theaqueous suspension of the synthetic carboxylated polymer are combined.

When mechanical stabiliser is used, in accordance with preferredembodiments, the mechanical stabiliser is added to the cross-linkingcomposition to maintain the multivalent metal complex ions in solution,to form a stabilised cross-linking composition, prior to addition of thecross-linking composition to the aqueous suspension of syntheticcarboxylated polymer.

In addition to, or in place of, the mechanical stabiliser, a surfactantmay be used to improve stability of the cross-linking composition. It isnot known to use a surfactant in the preparation of a cross-linkingcomposition in the art of the invention. Whilst surfactants may be addedto the latex composition, they are not combined in advance with thecross-linking composition for the purpose of maintaining a multivalentmetal in the cross-linking composition in solution as a negativelycharged multivalent metal complex ion. The cross-linking compositionneeds to be very stable to handle combination into the latex compositionin a manner that suits the production of the articles described herein.

Initially, a relatively highly concentrated cross-linking compositioncan be prepared. Relative amounts of components used in the productionof the concentrated cross-linking composition may be, per 100 parts byweight of water:

-   -   Between 0.01 and 5 parts of the (a) multimetal oxide of the        multivalent metal, the (b) hydroxide of the multivalent metal or        the (c) salt of the multivalent metal (preferably between 0.05        and 3 parts, or between 0.1 and 2 parts);    -   Between 0.01 and 5 parts of hydroxide (preferably between 0.05        and 4 parts when using component (a) above, between 0.05 and 3        parts when using component (b) above, or between 0.05 and 4        parts when using component (c) above); and    -   Between 0.03 and 15 parts of stabiliser (i.e. total stabiliser,        in the case of a mixture;

preferably between 0.5 and 3 parts).

There may however be some variation in the amounts shown above—these areindicative values that have been shown to work effectively.

After forming of the concentrated composition, this may be diluted priorto addition of the cross-linking composition to the aqueous suspensionof a synthetic carboxylated polymer. The dilution is usually performedto reduce the concentration such that the multivalent metal ionconcentration is reduced to between 0.33-3.3% by weight of thecross-linking composition. In this case, the amount is based on themetal ion, rather than the total weight of the source of multivalentmetal ions (a), (b) or (c). If considering the amount of the multivalentmetal source (i.e. (a), (b) or (c)) in the diluted cross-linkingcomposition, the diluted concentration of the source is typicallybetween 1-10% by weight of the cross-linking composition. As oneexample, the diluted concentration of sodium aluminate in thecross-linking composition may be about 5% (about 1.5% aluminium). Theinitial concentration of multivalent metal ions based on the abovetypical amounts in the concentrated cross-linking composition is around3 to 10% by weight.

Elastomeric Article-Forming Composition

The elastomeric article-forming composition comprises the cross-linkingcomposition, as described above, and a synthetic carboxylated polymer.The polymer is in the form of an aqueous suspension. The aqueoussuspension has a pH of at least 9.0. The elastomeric article-formingcomposition is also referred to as the “synthetic latex composition” or“latex composition”, as a short-hand reference. It is common in the artto use the expression “latex” or “rubber” to refer to any polymer in ageneral sense, and “latex composition” is used in a correspondingmanner. Latex is not to be read as referring to natural rubber latex.Accordingly, particularly in the examples which follow, it should beunderstood that these terms have been used as short-hand to refer to thepolymer of the composition.

The inventors found when performing their test work that the bestresults are obtained when a shock-increase in the pH of the latexcomposition (i.e. the aqueous suspension of the synthetic carboxylatedpolymer, as it is combined with other components to produce the latexcomposition) is avoided. This can be achieved in two ways. One wayinvolves very slow addition of the cross-linking composition to theaqueous suspension of the synthetic carboxylated polymer, to allow forequilibration of the pH without a shock increase in pH. (It is notedthat the higher the pH and concentration of the cross-linkingcomposition, the slower the addition rate, and vice versa.) The secondalternative is to ensure that the pH of the cross-linking composition isreasonably “matched” to the pH of aqueous suspension of the syntheticcarboxylated polymer. If the pH's are not too far apart, then the rateof addition is not as critical. Ideally, the matching involves bringingthe pH of both components (or streams) within 1.0 units, or between 0.5units of each other, preferably within 0.2 units of each other, and mostpreferably the same pH. However, as noted above, an even higher pHdifference is permissible if there is very slow addition if thecross-linking composition stream, and the cross-linking compositionadded is suitably stabilised with mechanical stabiliser and/orsurfactant. By adding the cross-linking composition as a diluted stream,at a slow rate of addition and/or with a matched pH, it is possible toproduce a latex composition from which there is no, or minimal,precipitation of the multivalent metal. (That is, there is less than20%, less than 15%, less than 10%, less than 5%, less than 2% andpreferably no precipitation of the multivalent metal from the latexcomposition).

Supply of an aqueous suspension of a synthetic carboxylated polymer to amanufacturing facility is usually in the form of a concentratedsolution, with a pH below 9.0. In the method of the invention, it may benecessary to add alkali to the aqueous suspension of the syntheticcarboxylated polymer prior to the addition of the cross-linkingcomposition to raise the pH of the aqueous suspension to at least 9.0.Alkali is referred to below in the list of other components that may bepresent in the latex composition, as a stabiliser. The amount should becontrolled to ensure the required pH for the aqueous suspension.

It may also be necessary to dilute the supplied aqueous suspension ofsynthetic carboxylated polymer to a total solids content (TSC) that iscloser to that required in the production of the elastomeric articles.For dipped articles, the final dipping TSC may be around 5-40%, and insome cases for thin film products, it may be between 5% and 25%, orbetween 5% and 20%. The initial dilution will be to a TSC that is alittle higher than the final dipping TSC concentration. The suppliedaqueous suspension of synthetic carboxylated polymer TSC typically needsto be at least about 5% higher than the TSC at which dipping isperformed, in view of the fact that the composition will be dilutedthrough the addition of the aqueous form of cross-linking composition ofthe present invention. Supplied latex may be provided at a TSC of around45%, around 50%, around 55% or around 60%, in some examples. The TSC atwhich the articles are formed (for example, the dipping or dippingcomposition TSC) may therefore be between 5-40%, 5-45%, 5-50% or 5-55%,respectively, for such supplied latex compositions.

Synthetic Carboxylated Polymer

The polymer used in the present application is a carboxylated polymer.The polymer is also synthetic, in that natural rubber (natural isoprene)is not within the range of polymers to which the invention applies.

The synthetic carboxylated polymer may be selected from the groupconsisting of carboxylated nitrile butadiene rubber, carboxylatedstyrene butadiene rubber, carboxylated butyl rubber, carboxylatedacrylic butadiene rubber, carboxylated polyisoprene, carboxylatedpolychloroprene, and mixtures or copolymers thereof. In someembodiments, the synthetic carboxylated polymer is carboxylatedacrylonitrile butadiene polymer, or a co-polymer of this polymer, or amixture of this polymer with a second polymer. In other embodiments, thesynthetic carboxylated polymer is a carboxylated syntheticbutadiene/chlorobutadiene polymer.

Carboxylated refers to the presence of carboxylate (carboxylic acid orester) groups on the polymer chain. Carboxylation may be achieved byforming the polymer with a monomer containing carboxylate groups, orthrough grafting carboxylate groups to a polymer. As examples ofsuitable carboxylated polymers, reference is made to PCT/AU2014/000726and PCT/AU2014/000727, the entirety of each being incorporated into thisspecification by reference.

As indicated below, the degree of carboxylation of the polymer mayinfluence the decision as to whether a second cross-linking agent isrequired. Where the carboxylation degree is 5-15% (more typically5-10%), then ionic cross-linking as provided by the cross-linkingcomposition of the invention may be sufficient to achieve the desireddegree of cross-linking and film properties. Thus, sulphur-free and/orzinc-free articles may be produced. Where the carboxylation degree islower, for example between 0.01-5%, then a second cross-linking agentmay be desirable. For calculating the % carboxylation, reference is madeto the above PCT publications. For mid-range carboxylation, the choicecan be made to have solely ionic cross-linking s provided by thecross-linking composition, or to have a second cross-linking agent too.Different embodiments take into account the different desired propertiesof the final article.

Adding of the Cross-Linking Composition to the Polymer Suspension

The cross-linking composition may be added to the aqueous suspension ofthe polymer in an amount of between about 0.01 and 0.5 parts per 100parts by volume of the aqueous suspension of the synthetic carboxylatedpolymer. The cross-linking composition is very dilute, so a relativelyhigh volume of dilute cross-linking composition is required. This isanother factor found to aid in the formation of a stable latexcomposition. The typical amount is amount in some embodiments is between0.03 and 0.3 parts (per 100 parts synthetic polymer suspension), and insome cases between 0.03 and 0.1 parts.

Prior to, or at the same time that the cross-linking composition isadded, it is advantageous to add surfactant to the aqueous suspension ofsynthetic carboxylated polymer. This aids to maintain the stability ofthe emulsion and the stability of the multivalent metal complex ions insolution. Such surfactants are additional to those that may be used inthe formation of the cross-linking composition, which may also beselected from the examples set out below.

The surfactant may be selected from anionic surfactants, non-ionicsurfactants, and combinations of agents from one or both classes.

Suitable anionic surfactants include, but are not limited to, (C₈-C₁₈)alkyl sulfates, (C₈-C₁₈) linear alkyl aryl sulfates, (C₈-C₁₈) alkylether sulfates, (C₈-C₁₈) fatty acid salts, (C₈-C₁₈) alkyl ether sulfateshaving one or more moles of ethoxylation, (C₈-C₁₈) alkyl ethersulfonates, sulfate esters of an alkylphenoxy polyoxyethylene ethanol,(C₈-C₁₈) alkamine oxides, (C₈-C₁₈) alkoyl sarcosinates, (C₈-C₁₈)sulfoacetates, (C₈-C₁₈) sulfosuccinates, (C₈-C₁₈) alkyl diphenyl oxidedisulfonates, methyl ester sulfonates, alpha-olefin sulfonates, alkylcarbonates, alkyl ether carboxylates, fatty acids, sarcosinates,octoxynol or nonoxynol phosphates, taurates, fatty taurides, fatty acidamide polyoxyethylene sulfates, isethionates and or blends thereof.(C₈-C₁₈) alkyl group may be straight chain (e.g., stearic, cetyl,lauric, oleic, myristic) or branched (e.g. 2-ethylhexyl). The cation ofthe anionic surfactant may be an alkali metal (e.g., sodium orpotassium), ammonium, C₁-C₄ alkylammonium (e.g., mono-, di-, tri-), orC₁-C₃ alkanolammonium (e.g., mono-, di-, tri-). The specific examples ofsuch anionic surfactants include, but are not limited to, laurylsulfates, octyl sulfates, 2-ethylhexyl sulfates, dodecyl benzenesulfonates, lauramine oxide, decyl sulfates, tridecyl sulfates,cocoates, lauryl sarcosinates, lauryl sulfosuccinates, lauryl ethersulfates (one or more ethylene oxides), myristyl sulfates, oleates,stearates, tallates, ricinoleates, cetyl sulfates and so forth.

Non-ionic surfactants include the following non-exhaustive examples:ethoxylated alkylphenols, ethoxylated and propoxylated fatty alcohols,polyethylene glycol ethers of methyl glucose, polyethylene glycol ethersof sorbitol, ethylene oxide-propylene oxide block copolymers,ethoxylated esters of fatty (C₈-C₁₈) acids, condensation products ofethylene oxide with long chain amines or amides, condensation productsof ethylene oxide with alcohols, and blend thereof. Specific examples,but are not limited to, methyl gluceth-10, PEG-20 methyl glucosedistearate, PEG-20 methyl glucose sesquistearate, C₁₁₋₁₅ pareth-20,ceteth-8, ceteth-12, dodxpol-12, laureth-15, PEG-20 castor oil,pollysorbate-20, steareth-20, polyoxyethylene-10 cetyl ether,polyoxyethylene-10 oleyl ether, polyoxyethylene-20 oleyl ether, anethoxylated nonylphenol, ethoxylated octylphenol, ethoxylateddodecylphenol, or ethoxylated fatty (C₆-C₂₂) alcohol, including 3 to 20ethylene oxide moieties, polyoxyethylene-20 isohexadecyl ether,polyoxyethylene-23 glycerol laurate, polyoxyethylene-20 glycerylstearate, PPG-10 methyl glucose ether, PPG-20 methyl glucose ether,polyoxyethylene-20 sorbitan monoesters, polyoxyethylene-80 castor oil,polyoxyethylene-15 tridecyl ether, polyoxy-ethylene-6 tridecyl ether,laureth-2, laureth-3, laureth-4, PEG-3 castor oil, PEG 600 dioleate, PEG400 dioleate, oxyethanol,2,6,8-trimethyl-4-nonyloxypolyethyleneoxyethanol,alkyleneoxypolyethylene-oxyethanol, alkyleneoxypolyethyleneoxyethanolwater soluble alcohol ethylene oxide condensates with C₈-C₁₈ carbonatoms in a straight or branched chain configuration with 5 to 30 molesof ethylene oxide and blends thereof. Other suitable nonionicsurfactants include the polyethylene oxide condensates of one more ofalkyl phenol containing C₈-C₁₈ carbon atoms in a straight or branchedchain configuration with 5 to 30 moles of ethylene oxide and blendsthereof. Specific examples of alkyl phenol ethoxylates include nonylcondensed with about 7-13/9.5 moles of ethylene oxide per mole ofoctyl/nonyl phenol, dinonyl phenol condensed with about 12/15 moles ofEO (ethylene oxide) per mole of phenol and mixtures thereof.

The surfactant is typically added as an aqueous solution. The solutionconcentration is typically around 2-10%. The amount of surfactantsolution that may be added to the aqueous suspension of the polymer withthe cross-linking composition may be such as to provide 0.01-5 phr tothe latex composition. The range may be between 0.1-2 phr, or about 0.6phr. It is noted that this surfactant is additional to any surfactantthat may be present in the concentrated aqueous suspension of syntheticcarboxylated polymer supplied by the supplier.

Other Components Added to Form the Elastomeric Article-FormingCompositions

Other components may be added to the latex composition, in addition tothe cross-linking composition and the surfactant. These other componentsmay include components selected from the group consisting of secondcross-linking agents, plasticizers, anti-ozonants, stabilisers such aspH stabilisers, emulsifiers, antioxidants, vulcanising agents,polymerisation initiators, pigments, fillers, colourising agents andsensitisers. Many of these agents are added in particulate form. Othersare added as liquids. These are added prior to forming the latexcomposition into the shape of the synthetic elastomeric article. In someembodiments they are added at the same time as the cross-linkingcomposition. In other embodiments, they are added after.

Second Cross-Linking Agent

Although in some embodiments it is possible to use the cross-linkingcomposition containing solubilised multivalent metal as the onlycross-linking agent, in other embodiments a second cross-linking agentwill be added. This is added as a separate component during theformation of the latex composition. This is typically added as a solid,particularly in the case of ionic cross-linking agents and sulphur. Theparticulate cross-linking agents may be added to the aqueous suspensionof the synthetic carboxylated polymer at the same time as thecross-linking composition, or following addition of the cross-linkingcomposition.

The multivalent metal of the cross-linking composition provides ionicbonding only, so in some embodiments, to provide covalent bonding,sulfur and sulfur donating crosslinking agents are recommended as secondcross-linking agents. Such covalent bonding may provide water resistantcharacteristics due to its hydrophobic nature and will have moreendurance at aqueous conditions. Thus, where the degree of carboxylationis low, a covalent cross-linking agent may be desired.

The second cross-linking agent may be a single type of cross-linkingagent, or there may be more than one such second cross-linking agent.Each may be referred to as a second cross-linking agent, or they may bereferred to as a second, third (and optionally further) cross-linkingagents.

The covalent cross-linking agent may be selected from the covalentcross-linking agents, including organic cross-linking agents, sulphurand/or sulphur donors, and combinations thereof.

The cross-linking agents may be selected from the above describedcovalent cross-linking agents, ionic cross-linking agents, andcombinations thereof.

Amongst the range of cross-linking agents, the following may be used inembodiments of the invention:

Sulphur may be added in the form of elemental sulphur. Sulphur donorsare another way of providing sulphur cross-linking. Sulphur donorsrelease sulphur, or act with sulphur-containing compounds, to acceleratesulphur-based covalent cross-linking of the elastomer-forming polymer.Generally, sulphur donors can be advantageous as they shorten the curing(vulcanisation) time, lower the curing temperature or decrease theamount of cross-linking agents required to be used in the composition.However, on the negative side, sulphur donors can give rise to allergicreactions, such as allergic contact dermatitis with symptoms includingerythema, vesicles, papules, pruritus, blisters and/or crusting.Examples of suitable sulphur donors include the carbamates such asthiocarbamates (e.g. zinc dibutyl dithiocarbamate (ZDBC), Zinc diethyldithiocarbamate (ZDEC); Zinc dimethyl dithiocarbamate (ZDMC); thiurams(eg. tetraethylthiuram disulfide (TETD), Tetramethylthiuram disulphide(TMTD)); Dipentamethylene thiuram tetrasulfide (DPTT); Dipentamethylenethiuram hexasulfide (DPTH); Dipentamethylene thiuram hexasulfide;thiourea (Ethyl thiourea (ETU) and diphenylthiourea (DPTU); thiazoles(e.g. Mercapto Benzothiazoles (MBT), Mercapto Benzothiozole disulphide(MBTS), zinc 2-mercaptobenzothiazole (ZMBT)); guanidines (eg.Diphenylguanidine (DPG)) and aldehyde/amine-based sulphur donors (eg.hexamethylenetetramine). Other examples are well known in the art andcan be obtained from various publicly available sources.

In some notable embodiments, the second cross-linking agent compriseseither (a) sulphur and a sulphur donor, (c) sulphur and a sulphur donortogether with an ionic cross-linking agent, or (d) a sulphur donor. Inthese embodiments, the second cross-linking agents may consist of thesecross-linkers as the only additional cross-linking agents. (In thatcase, the cross-linking composition may comprise the solubilisedmultivalent metal oxide, hydroxide or salt, as the only cross-linkingagents of said cross-linking composition. Further, in example (a), thecomposition is free of solid metal oxide cross-linking agent, and in thecase of (d), the composition may be free of sulphur and free of solidmetal oxide cross-linking agent). In another embodiment, the secondcross-linking agent comprises (b) a multivalent metal oxide or ioniccross-linking agent. In this embodiment, the product is free of sulphurand sulphur donor.

In other embodiments, other cross-linking agents that are suitable foruse in the elastomeric film-forming composition are selected from, butare not restricted to crosslinking monomers, reactive oligomers,polyisocyanate oligomers, functional, crosslinkable polymers,derivatives of ethylene glycol di(meth)acrylate (such as ethylene glycoldiacrylate, di(ethylene glycol) diacrylate, tetra(methylene/ethyleneglycol) diacrylate, ethylene glycol dimethacrylate (EDMA), di(ethyleneglycol) dimethacrylate (DEDMA), tri(methylene/ethylene glycol)dimethacrylate, tetraethylene glycol dimethacrlate (TEDMA)), derivativesof methylenebisacrylamide (such as N,N.-methylenebisacrylamide,N,N.-methylenebisacrylamide, N,N.-(1,2 dihydroxyethylene)bisacrylamide),formaldehyde-free crosslinking agents (such asN-(1-Hydroxy-2,2-dimethoxyethyl)acrylamide), divinylbenzene,divinylether, diallyl phthalate, divinylsulfone, TrimethylolpropaneTrimethacrylate (TMPTMA) and the like. Some of these cross-linkingagents are commercially available and are supplied by companies such asAldrich. Combinations of these cross-linking agents can also be used.

To get the better uniformity of the film and properties thereof and polyfunctional cross linkers could also be used, some poly functional crosslinkers are (but not limited to) diphenylmethane-bis-4,4′-N-ethyleneurea, N,N′-1,6-hexanediylbis-1-aziridinecarboxamide, pentaerythritoltris(3-(1-aziridinyl) propionate, trimethylolpropane tris(2-methyl-1-aziridine propionate,trimethylolpropane-tris-(B—N-aziridinyl) propionate, multifunctionalmethacrylate monomers like ethylene glycol dimethacrylate, triethyleneglycol dimethacrylate, trimethylolpropane trimethacrylate—simple organiccross linkers like water soluble glyoxal could be used—these willimprove adhesion of water based systems to non-polar substrates atmolecular level and thereby making the film formation better and freefrom cracks.

Solid ionic cross-linking agents are another class that may be added.This class includes solid metal oxide cross-linking agents, such as zincoxide and magnesium oxide. In some (but not all) embodiments, they areavoided (thus, zinc oxide may be avoided), to avoid the costs anddisadvantages described previously. However, when used in low amounts,they can provide additional properties that may be useful in someapplications. Metal oxides (particularly when used in solid form) aretypical examples, including zinc oxide and magnesium oxide. Peroxidesalso form ionic cross-links. An example of a peroxide cross-linkingagent is 1,1-di(t-butylperoxy)-3,3,5-trimethylcyclohexane, which can bepurchased under the trade name Trigonox 29-40B-pd. Other ioniccross-linking agents amongst those known in the art can be used.

When a second cross-linker is present, in some embodiments, this isselected from the group consisting of sulphur, organic peroxide, organiccross-linkers, sulphur donors and combinations thereof. This groupingexcludes the solid inorganic ionic cross-linkers.

In embodiments shown to have particular utility in commercialproduction, the second cross-linking agent may be selected from either:

(a) sulphur and a sulphur donor,(b) a multivalent metal oxide or ionic cross-linking agent (zinc oxidebeing a notable example),(c) sulphur, a sulphur donor and an ionic cross-linking agent, or(d) a sulphur donor.

The examples show the utility of these cross-linking agents as the onlycross-linking agents used in combination with the cross-linkingcomposition. In such cases, other cross-linking agents may be avoided,but small amounts (below 0.01 phr) should not be considered to avoid thescope of such a claim.

Amounts of Second Cross-Linkers

In broad terms, any amount of second cross-linker may be used, asrequired for the final article properties. Thus, the total amount ofcross-linking agents in the composition (including that added in theformation of the cross-linking composition) may be between 0.01 and 14phr. However, it is usually desirable to minimise cross-linker amounts(and the associated costs or disadvantages). With the use of thecross-linking composition of the present invention, this is possible.The total cross-linking agent amount (including that used to form thecross-linking composition) may be within one of the following ranges:0.01-14.5 phr, 0.2-12.5 phr, 0.3-10 phr, 0.1-10 phr, 0.2-10 phr, 0.3-9phr, 0.5-9 phr, 0.8-9 phr, 0.3-8 phr, 0.5-8 phr, 0.8-6 phr, 1-5 phr, 2-9phr, 3-10 phr, 3-7 phr, 1-3 phr, 0.01-0.5 phr, 0.01-1.0 phr.

In desirable embodiments, the amount of each secondary cross-linker ispreferably not more than 1.0 phr, preferably not more than 0.9, 0.8.0.7, 0.6, 0.5, 0.4, 0.3 or 0.2 phr. The total amount of all secondarycross-linkers is preferably also not more than (or is below) 1.0, 0.9,0.8. 0.7, 0.6, or 0.5 phr.

The amount of sulphur, when used as a second cross-linker, may bebetween 0.0-5.5 phr. The amount may be lower still, at 0.0-3.5 phr, suchas 0.01-3.0 phr, 0.01-2.0 phr, 0.01-1.5 phr, 0.01-1.0 phr or 0.01-0.5phr. The amount is preferably not more than 1.0 phr, preferably not morethan 0.9, 0.8. 0.7, 0.6, 0.5, 0.4, 0.3 or 0.2 phr.

The amount of sulphur donor, when used as a second cross-linker, may bebetween 0.0-2.0 phr, such as between 0.1-1.5 phr, 0.1-1.0 phr, 0.2-1.0phr, 0.3-2.0 phr, 0.3-1.5 phr or 0.2-0.6 phr. The amount is preferablynot more than 1.0 phr, preferably not more than 0.9, 0.8. 0.7, 0.6, 0.5,0.4, 0.3 or 0.2 phr.

The amount of organic cross-linking agent, when used as a secondcross-linker, may be between 0.0-4.0 phr, such as 0.01-4.0. The amountmay be lower still, at 0.01-3.0 phr, or 0.01-2.0 phr, or 0.01-1.0 phr.

The amount of ionic cross-linking agent, when used as a secondcross-linker, may be between 0.0-4.0 phr, such as 0.01-4.0. The amountis preferably lower still, at 0.01-3.0 phr, or 0.01-2.0 phr, 0.01-1.0phr or 0.01-0.5 phr. This applies to solid multivalent metal oxides suchas zinc oxide. The amount is preferably not more than 1.0 phr,preferably not more than 0.9, 0.8. 0.7, 0.6, 0.5, 0.4, 0.3 or 0.2 phr.

Other Components

Stabilisers may be used in the elastomeric article-forming composition.The stabilizer may be, for example, an anionic surfactant and or othernon-ionic surfactants. The elastomer-forming polymer can be diluted witha solution of a stabilizer, such as potassium hydroxide, ammoniumhydroxide and/or sodium hydroxide. The amount of stabiliser used isdependent on the polymer used in the elastomeric film-formingcomposition, the pH of the composition and other factors. The stabilisercan range from 0.1-5.0 phr, e.g. 0.5 to 2 phr, preferably 1.0 to 1.5phr, which is diluted with water, preferably filtered water- orde-ionized water, or water having a total solid content of around 5 ppmlevel.

Emulsifiers may be used in the elastomeric article-forming composition.Suitable emulsifiers include comprise sodium alkyl aryl sulphates,sodium alkyl sulphates or other anionic/non-ionic surfactants. Theamount of emulsifier used is dependent on the on the polymer used in theelastomeric film-forming composition, the pH of the composition andother factors. The amount of emulsifier can range from about 0.1 to 3phr.

pH stabilisers may be used to avoid the possibility of destabilization,which is possible where the polymer contains carboxylic acid groups.Suitable pH stabilisers include potassium hydroxide, ammonium hydroxideand/or sodium hydroxide. Preferably, the pH stabiliser is potassiumhydroxide. A diluted stabilizer solution can be mixed with the polymer.The pH of the mixture is suitably adjusted to between about 8.5 to about12.5, or between about 8.5 to about 11.0. The cross-linking agent(s) canthen be added to the mixture.

Anti-ozonants may be used in the elastomeric article-formingcomposition. Suitable anti-ozonants include paraffinic waxes,microcrystalline waxes and intermediate types (which are blends of bothparaffinic and microcrystalline waxes). The amount of anti-ozonant canrange from about 0.0 to 5.0 phr.

Antioxidants may be added to the elastomeric article-forming compositionof the present invention. Suitable antioxidants include hinderedarylamines or polymeric hindered phenols, and Wingstay L (the product ofp-cresol and dicyclopentadiene). The antioxidant may, for example, beadded in an amount ranging from 0.0-5.0 phr, 0.0-3.0 phr, 0.0-1.0 phr or0.3-0.5 phr.

Pigments such as titanium dioxide, selected for its pigmentation, toreduce the transparency of the final elastomeric film, may be added inamounts ranging from 0.01-10.0 phr, such as 1.5-2.0 phr or 1.0-3.0 phrand colorants can also be added in the desired amounts. The mixture isthen diluted to the target total solids concentration by the addition ofa liquid, such as water. The pigments used in the elastomericfilm-forming composition may be selected from the group consisting ofEN/USFDA approved dyes.

Rubber reoderants may be used in the elastomeric article-formingcomposition. Suitable rubber reoderants include perfume oils of naturalor synthetic origins. The amount of rubber reoderant can range fromabout 0.001 to 2.0 phr.

Wetting agents may be used in the elastomeric article-formingcomposition. Suitable wetting agent emulsifiers include anionicsurfactants like sodium dodecyl benzene sulfonate or sodium lauryl ethersulfate, or non-ionic ethoxylated alkyl phenols such as octylphenoxypolyethoxy ethanol or other non-ionic wetting agents. The amount ofwetting agent can range from about 0.001 to 2.0 phr.

Defoamers may be used in the elastomeric article-forming composition.Defoamers may be chosen from naphthalene type defoamers, silicone typedefoamers and other non hydrocarbon type defoamers or defoamers ofrefined oil of vegetable origin. The amount of defoamers can range fromabout 0.001 to 2.0 phr.

The elastomeric article-forming composition could also be blended withinorganic filler. Suitable inorganic fillers include calcium carbonate,carbon black or clay. Preferably, the amount of inorganic fillerincluded in the blend would not exceed 75% either alone or incombination. It will be appreciated that the blended composition willretain the favorable properties.

The elastomeric article-forming composition comprising carboxylatedsynthetic polymer more specifically and multi metallic oxide andadditives thereof could also be blended with another alternativeelastomer. For example, the alternative elastomers, for specificintended application like physical properties, permeationcharacteristics, film uniformity. Examples of suitable alternativeelastomers include styrene butadiene rubber and butyl rubber,polyisoprene and mixtures thereof. Preferably, the amount of alternativeelastomers included in the blend would not exceed 95% either alone or incombination. In some embodiments, an elastomer is present in an amountof from 0 to 95%. The range could be 0-5%, 5-10%, 10-15%, 15-20%,20-25%, 25-30%, 30-35%, 35-40%, 40-50%, 50-60%, 60-75%, 60-80%, 70-90%or 80-95%. It will be appreciated that the blended composition willretain the favourable intended properties to the applications concerned.

Sensitisers are chemicals that can be used in compositions for producingelastomeric films to control the amount of the composition that willremain coated on the mould during dipping (film deposition). Examples ofsensitisers known in the art that can be used in the composition forproducing an elastomeric film include polyvinyl methyl ether,polypropylene glycol, ammonium nitrate and ammonium chloride. When used,the amount of sensitiser will be chosen based on the desired filmthickness to remain on the mould during dipping, and will generally bebetween 0.01-5.0 phr. For thinner films, the amount will generally bebetween 0.01 to 2.0 phr, e.g. 0.1 to 1.0 phr. When other techniques areused for controlling the film thickness on the mould, such as the use ofpre-dipping the mould into coagulant before undertaking the multipledipping into the composition for producing the elastomeric film, thecomposition for producing an elastomeric film may not require asensitiser.

Those skilled in the art will readily be able to vary the components ofthe elastomeric article or film-forming composition to suit theparticular polymer used as well as the particular final article desired.It will also be understood by those of skill in the art that specificchemicals or compounds which have been listed above are intended to berepresentative of conventional materials that may be used in formulatingthe elastomeric film-forming composition and are merely intended asnon-limiting examples of each such component of the composition.

The elastomeric article-forming composition is preferably formalin-free.

Final Composition Preparation Stages

The steps in the production of the cross-linking agent, and the mainsteps in the formation of the latex composition, have been describedabove. In other respects, the process steps for the production of thearticle are as known or practiced in the art.

By way of additional comment, it is noted that in the case of thepresent invention, the cross-linking composition provides themultivalent metal in a solubilised form, and any second cross-linkerswhich are in solid form are added following milling. Milling isperformed using suitable milling equipment to reduce the particle sizeto a suitable range. Preferably, the average particle size is below 5microns. Uniform particle size is desirable, and coarse milling mayresult in non-uniform particles and therefore a non-uniform film, whichcan result in high fluctuation in film properties.

After the desired pH is reached for the aqueous polymer suspension(above 9.0, such as 9.0 to 12), the cross-linking composition is added.Any shock increase in the pH during addition of the cross-linkingcomposition will result in coagulation from micro level to the macrolevel.

When the components have been mixed uniformly or to homogeneity, otheradditives such as pigments and colorants are added. The elastomericarticle-forming composition is then left for maturation. The length ofthe maturation may vary depending on the level of cross-linking agentand the degree of carboxylation of the polymer. The cross-linkingcomposition-containing suspension of the carboxylated synthetic polymerdoes not require lengthy maturation since the condensation reaction istheoretically rapid. However, the composition may be left for a minimumof 2 to 18 hours for the purpose of removing air bubbles inside thecompounded polymer. In some cases maturation could be conducted over alonger period depending upon the requirements for preparing the articleand the level of cross-linking agents present. The compoundedelastomeric film composition with suitable additives could be prematured(in view of other crosslinkers involved in the composition) by holdingthe composition at a controlled elevated temperature. For example, theelastomeric article-forming composition could be held at 40° C. to 60°C. for a period of, for example, about 4 hours to about 24 hoursdepending on the temperature, degree of carboxylation of the polymer,the amount and type of vulcanization activators and sulphur donors, andtype and quantity of pH stabilizer and emulsifier stabilizer and wettingagents/surfactants.

Preparation of Elastomeric Articles, Such as Films

The composition is formed into the shape of the desired article, andthen cured. Curing is used in a general sense, to refer to the stageduring which cross-linking is performed. The curing step includes theprocess of cross-linking of the multivalent metal in the cross-linkingcomposition with the carbon/late groups of the polymer. Other curingconditions may apply, such as the conditions required for curing thesecond cross-linking agents. Such conditions are as known in the art.

The forming of the product into the desired shape may involve mouldinginto a mould, depositing the composition onto a surface, or dipping of aformer into the composition. The composition is particularly suited todipping applications. Films can be produced by dipping, and gloves inparticular. Thin film gloves are a desirable product.

The steps in the manufacture of a film, as an example of an article thatmay be formed from the composition, film are as generally described inPCT/AU2014/000726 and PCT/AU2014/000727, other than the filmcompositions.

The basic process steps in some embodiments are as follows:

Optional Step (a) Dipping the Former into a Coagulant ContainingMultivalent Ions in Solution

The details of this step are as described in the PCT publicationsreferred to above. In brief, a suitable former, which is based on theshape of the article to be produced (e.g. flat for a film orglove-shaped for a glove) can be dipped into a coagulant containingmultivalent ions in solution. The former is dipped into a coagulantcontaining multivalent ions, leaving a thin coating of the charged ionson the surface of the former. The charged ions coating can assist incontrolling the amount composition for forming the elastomeric film thatwill subsequently remain on the surface of the mould after dipping intothe composition, through charge interactions. The composition of thecoagulant may be as described in the two PCT publications as describedabove. Cationic multivalent ion-containing coagulants are typicallyused, such as a calcium coagulant.

Optional Step (b) Drying or Partially Drying the Coagulant-Dipped Former

If the former is dipped into a coagulant, following this step the formeris dried or partially dried.

Step (i) Dipping the Former into the Elastomeric Article-FormingComposition of the Invention to Produce a Layer of ElastomericArticle-Forming Composition on the Mould

The former is dipped into the composition for producing an elastomericfilm, embodiments of which have been described in detail above. Theduration of dipping, temperature, and former surface temperature may beas described in the PCT publications referred to above.

Step (ii) Drying or Partially Drying the Layer of ElastomericFilm-Forming Composition on the Former

The conditions and details of this step may be as described in the PCTpublications referred to above.

The method of manufacture described herein encompasses the preparationof single-layered or multiple-layered elastomeric films. Therefore, insome embodiments, the method may include step (v), which involves dryingand curing the layered elastomeric film on the former directly afterthis step to prepare a single layered elastomeric film. In otherembodiments, the method may include a number of repetitions of optionalsteps (iii) and (iv) after this step to produce a multiple-layeredelastomeric film.

Step (iii) Optionally Dipping the Former Coated with the Dried orPartially Dried Layer of Elastomeric Film-Forming Composition into theElastomeric Film-Forming Composition to Produce a Further Layer ofElastomeric Film-Forming Composition on the Former

This step is optional, and is present when multi-layer articles areproduced. The details of this step are as described in the PCTpublications referred to above.

Step (iv) Optionally Repeating the Drying or Partial Drying Step (ii)and the Further Dipping Step (iii)

This step is optional, and is present when multi-layered articles areproduced. The number of layers may be 2, 3 or more in multi-layeredarticles. The details of this step are as described in the PCTpublications referred to above.

Optional Additional Steps Prior to Drying and Curing

Further steps can be taken to fine-tune the manufacture of theelastomeric film or article. The details of these steps are as describedin the PCT publications referred to above. In brief, the film or articlecan be leached to remove extractable components, there may be a coatingmaterial applied, beading/cuffing cab be performed and/or the productmay be passed through a curing or vulcanizing oven to evaporate thewater in the film and enable better cross linking.

Step (v) Drying and/or Curing the Layered Elastomeric Film on the Former

The details of this step are as described in the PCT publicationsreferred to above.

Optional Additional Steps Following Drying and Curing

This step is optional. The details of this step are as described in thePCT publications referred to above. These optional steps includecooling, chlorination, post-curing rinsing, polymer coating andadditional drying steps, prior to stripping the article from the former.The cured film may also be cooled/chlorinated/neutralized—post-leachedin hot water and optionally dipped in lubricant solution or anysilicone/silicone free polymers to enable easy stripping and betterdonning.

The film or article is stripped from the former at the conclusion of theformation process.

Articles Produced from the Elastomeric Film-Forming Composition

The elastomeric article-forming composition of the present invention canbe used to prepare a variety of articles, including dipped articles inparticular. Examples of possible articles include surgical andexamination gloves, industrial gloves, finger cots, catheters, tubing,protective coverings, balloons for catheters, condoms, industrialgloves, laboratory gloves, household gloves, gardening gloves,electrical gloves, irradiation gloves, finger cots, weather balloons,clean room gloves for electronic industries, gloves for food contact andfood processing and biotechnical application and the like.

The thickness of the final film (or article) can, for example, be in therange 0.01-3.0 mm, such as 0.01-0.3 mm, less than 0.25 mm, less than0.24 mm, less than 0.23 mm, less than 0.22 mm, less than 0.21 mm, lessthan 0.2 mm, 0.02-0.2 mm, less than 0.19 mm, less than 0.18 mm, lessthan 0.17 mm, less than 0.16 mm, less than 0.15 mm, 0.05-0.10 mm,0.03-0.08 mm, or 0.05-0.08 mm (for thin or disposable gloves), and0.2-3.0 mm for thick gloves. The thickness is suitably measured as an“average thickness”, particularly for gloves, using the points ofmeasurement described below. The points of measurement are at threepoints in the glove, and an average of the three values may be taken forthe (average) film thickness. A corresponding technique can be used fornon-glove articles, such as condoms. In some embodiments, the filmthickness of a glove is less than 2 mm (e.g. from 0.01 mm to 2 mm). Forexample, the film thickness may be in the range of from 0.04 mm to 2 mm.In another embodiment, the glove may have a weight of about 4 grams, orabout 3 grams, while it will be appreciated that higher and lower gloveweights may also be obtained depending on the purpose for which theglove is to be used. The weight may be, for instance not more than 5grams, not more than 4.9, 4.8, 4.7, 4.6, 4.5, 4.4, 4.3, 4.2, 4.1 or 4.0grams on average. This calculation may be based on a sample of at least10 gloves.

The final film (or article) can, for example, have one layer or be madefrom multiple layers produced by subsequent dipping steps. For example,the final film (or article) may comprise from 1 to 15 layers.

The final film prepared from the elastomeric film-forming composition ofthe invention retains the favourable feel and comfort that is closer tonatural rubber film yet is free of proteins and other potentialallergens (causing Type I allergy) associated with natural rubber. Insome embodiments, the final film prepared from the elastomericfilm-forming composition of the invention has reduced skin irritationcompared to natural rubber film. For example, the final film preparedfrom the elastomeric film-forming composition of the invention reducesthe risk of Type I allergy compared to natural rubber film. Preferably,the film prepared from the elastomeric film-forming composition of theinvention avoids Type I allergy. Where the dipped article is a glove,retaining the properties of natural rubber gloves also means that theproducts are easily donnable without any visible powder anti tackmaterial. Like natural rubber gloves, the gloves of the presentinvention could be easily donnable without any visible powder anti tackmaterial like talc, corn starch or calcium carbonate however containspolymeric laminate of acrylate on the interior surface of the glove orchlorinated. However production of pre-powdered article is also possiblewith the less amount of powder content required by the standardconcerned or the customer requirement. Further, proper curing of thefilm removes tackiness, and the bonding characteristics of the polymercomprising base polymer unit/s acrylonitrile butadiene, styrenebutadiene, chlorobutadiene—one or more carboxylic acid residues oresters thereof makes the common coating material sufficient enough forproper donning and non-tacky effect and suitable powder free conditions.

The articles produced by the method have a desirable balance ofproperties. In typical embodiments, the articles have a modulus at 500%of less than 7 MPa. The modulus at 500% may be not more than (or lessthan) 6.5 MPa, or even less than 6.4, 6.3, 6.2, 6.1, 6.0 or lower. Thisvalue may be based on the unaged variant, but is preferably based on theaged variant, or both the unaged and aged variants. Having such a lowmodulus, in combination with a thin glove (e.g. one of the valuesindicated above, such as 0.2 mm or less), is an excellent achievementfor such gloves. The articles may have an elongation at break of atleast 700%. The articles of typical embodiments have these propertiescombined. In some embodiments, the article is chloroprene-free, and hasa modulus at 500% of less than 7 MPa (or less than 6.5) and anelongation at break of at least 700%. IN other embodiments, there isprovided articles, such as gloves, with an elongation at break of atleast 700% combined with thin film thickness (of 0.2 mm or less). Theproduction of articles with these properties, particularly with low (orno) second cross-linking agents, is a notable feature of embodiments ofthe present invention.

In the claims and in the preceding description, except where the contextrequires otherwise due to express language or necessary implication, theword “comprise” or variations such as “comprises” or “comprising” isused in an inclusive sense, i.e. to specify the presence of the statedfeatures but not to preclude the presence or addition of furtherfeatures in various embodiments of the invention.

Examples

The invention will now be described in further detail with reference tothe following non-limiting examples which involve the preparation ofelastomeric film gloves as the elastomeric articles.

General Procedure for Production of Elastomeric Articles

In the examples set out below, the following general procedure wasutilised to produce elastomeric gloves, unless indicated to thecontrary.

1. Preparation of Cross-Linking Composition

One part sodium aluminate as the chosen multivalent metal source,together with 1 part sodium hydroxide and 1 part potassium hydroxide asalkali and 1 part glycerine as stabiliser, were combined with 46 or 96parts water, depending on the example. The combination was heated at anelevated temperature (typically around 95° C., but anywhere from 80° C.to boiling point) to dissolve the multivalent metal, through theformation of negatively charged multivalent metal complex ions. Theconcentration of metal ions in the cross-linking compositions obtainedwas 0.66% or 0.33% by weight of total solution, respectively. The pH ofthe solution was in the range of about 12-13.

2. Preparation of Latex Composition

A commercially-available aqueous suspension of synthetic carboxylatedpolymer, supplied at a total solids content of about 45%, is diluted toan intermediate total solids content using 3% potassium hydroxidesolution. The amount of potassium hydroxide solution added was such asto provide the amount of KOH indicated in the examples (phr). The actualtotal solids content to which the suspension is diluted is chosen basedon the desired phr amount of KOH and the final total solids content ofthe dipping composition for the latex composition. The final totalsolids content may be anywhere between 13% and 35%. For a final latexcomposition having a total solids content of about 20%, as used in theseexamples, the initial dilution is to about 25%-30%. The pH of thediluted suspension so produced was above 9.0, typically in the range of9.2 to 9.6.

The diluted suspension of synthetic carboxylated polymer is placed in amixing vessel, and the surfactant is added. The amount and identity ofthe surfactant was as indicated in the examples. Next the cross-linkingcomposition added very slowly with constant stirring. The cross-linkingcomposition is added in an amount to provide the required phr ofmultivalent metal to the polymer. In view of the concentrations of thestreams used in the examples, the relative amounts of the two componentswas about 0.1 parts of cross-linking composition to 100 parts polymersuspension. This further reduces the total solids content of the polymercloser to 20%.

Next, any second cross-linking agents were added. The sequence ofaddition was as follows. First, any solid zinc oxide or magnesium oxidewas added (if used). Second, liquid-form second crosslinking agents wereadded (such as glyoxal in the glyoxal examples). Third, sulphur andsulphur donors were added.

Finally, a dispersion in water of final powder materials was added. Thisincluded the titanium dioxide and antioxidant. The amount of inclusionof each is as required to provide the target formulation for the latexcomposition. After addition of the solid components, the pH maybe finetuned by the addition of further alkali (the 3% KOH solution in thepresent examples). The total solids content of the final formulation forthe latex composition for the examples was about 20%. In other cases, itmay be between 5% and 40%, or between 5% and 20% for the formation ofthin film articles.

3. Washing

The formers are subjected to pre-washing, to remove any remainingresidues following removal of a glove previously made on the former. Theformers are cleaned in mild acid/alkali and hot water. The formers arethen dried by blowing air by blowers or air curtains or using ovens withthe hot air having temperature above 105° C.

4. Coagulant Dipping

The cleaned dry former is immersed in a coagulant bath, which contains a0-50% by weight solution of calcium nitrate. The coagulant also contains0.1%-5.0% by weight metallic stearates, suitable wetting agents(0.001-1.0%) and antifoaming agents (0.001-1.0%). In some embodiments,coagulant dipping is not required. In the examples practiced here, thecoagulant contained 1-13% calcium nitrate, 0.5-1.5% metallic stearate,0.08-0.12% wetting agents and 0.005%-0.01% anti-foaming agent.

5. Drying

The coagulant coated formers are dried in a hot air circulated oven at atemperature of about 110° C. to 130° C.

6. Dipping Step

The former, coated with dried coagulant, is dipped into a tankcontaining the latex composition described in step 2 above. Thecomposition is maintained at temperature of around 20-35° C., and isconstantly circulated in the tank to avoid creaming and settling of thesolids. The former is dipped into the composition for a dwell time ofbetween 5 and 60 seconds. In the examples practiced here, the dwell timewas 8 seconds.

7. Drying

The composition coated formers are gelled in a gelling oven at atemperature of about 100-300° C. and the duration of 2-300 seconds. Inthe examples practiced here, the drying conditions were 110° C. for 60seconds.

8. Pre-Leaching

Pre-leaching is conducted by rinsing in warm water for a short period oftime. The gelled film coating on the former is pre-leached in series oftanks at a temperature anywhere between ambient and 95° C. In theexamples it was typically about 55° C. In the case of single dipping ofelastomer, preleaching is completed as per this sequence. In case ofmultiple dipping of latex composition, this is completed after the finaldip into the latex composition followed by gelling.

9. Second Dipping Step

The gelled elastomeric film coating on the former is dipped into a tankcontaining the latex composition, which contains the componentsspecified for the given example (as prepared through step 2). Thecomposition is maintained at temperature of around 20-40° C., and isconstantly circulated in the tank to avoid creaming and settling ofsolids. The former is dipped into the composition for a dwell time of5-90 seconds. In the examples practiced here, the second dip dwell timewas 8 seconds.

10. Gelling/Pre Leaching/Beading

The product following the second dipping step is subjected to gellingand pre-leaching and beading. In the case of on-line polymer coating thesequence is gelling/preleaching/polymer coating/beading.

The beading, drying and pre-leaching steps can be carried out in anyorder. The processes of beading and pre-cure leaching could be exchangedepending on the quality of cuff beading.

11. Curing

The beaded glove is then cured. Curing was conducted at about 80°C.-150° C. for about 15-30 minutes, depending upon the film thicknessand intended end product physical properties.

12. Post-Leaching/Lubricant/Final Drying/Stripping/Tumbling

In the case of a glove product, the cured elastomeric article may besubjected to one or more process steps including post-leaching,chlorination (noting that this could alternatively take place beforecuring), neutralisation, additional curing/surface treatment and/orlubricant application (e.g. through dipping into a lubricantcomposition). The gloves will be stripped from the former and dried.Packaging may follow. Where additional curing or surface treatment isrequired, the gloves could be tumbled using hot air at a temperaturearound 80-120° C. for about 15-120 minutes.

Test Procedure

For all of the Examples, tests were performed to determine the followingproperties of the films:

-   -   Modulus at 300%    -   Modulus at 500%    -   Tensile strength (MPa/Psi) (1 MPa=145 Psi); and    -   Elongation %.

Tensile strength, stress at 300% and 500% modulus and elongation tobreak were measured by testing procedures conducted in accordance withASTM D 412-06a (2013), based on the sample size set by the standard forgloves. The gloves were also tested for force at break measured inaccordance with EN 455. The standards are readily available. These testscan be applied to multilayer films and gloves (such as examinationgloves for medical applications). In all tables of results, the valuesindicated for the tensile strength, modulus at 300% and modulus at 500%are in units of MPa, and the elongation (or elongation at break) in %.

General Formulation Set out below is a typical formulation for thecomposition.

Parts per Hundred Rubber (phr) - Dry basis Ingredients (unless otherwiseindicated) Carboxylated synthetic polymer or 100 blend Alkali 0.1-2.0Sufficient to provide a pH of at least 9.0 Cross-linking composition,comprising: Added in an amount to provide the following: negativelycharged multivalent metal 0.01-5.0, based on weight of complex ionsmetal ion per hundred parts rubber, by weight alkali to solubilise andform the 0.1-5.0 negatively charged multivalent metal Sufficient toprovide a pH complex ions in the cross-linking of at least 9.0composition (providing a pH of at least 9.0 to the cross-linkingcomposition) mechanical stabilizer for maintaining  0-5.0 the metalcomplex ion in solution Emulsifier stabilizers 0.1-5.0 Antiozonant0.0-5.0 Covalent cross-linking agent 0.0-4.0 Insoluble ioniccross-linking agent 0.0-4.0 Sulphur and Sulphur donor cross- 0.0-5.5linking agents Antioxidant 0.2-3.0 Opaqueness provider 0.0-5.0 (whenpresent, 0.01-5.0) Pigment As per requirement Defoamer 0.001-2.0 

EXAMPLES

In each of the examples, other than comparative examples, across-linking composition was prepared from selected components of theoverall formulation indicated, using step 1 of the general procedureoutlined above. The cross-linking composition was combined with acommercially available carboxylated synthetic polymer (the identity ofwhich is outlined in the examples), in accordance with steps 2 and 3 ofthe general procedure, in amounts to produce the latex compositions setout in the relevant table. A film was produced using the steps of thegeneral procedure from the latex composition.

Example 1—Sodium Aluminate

Films were produced using the compositions shown below, each containingsolubilised aluminium.

Composition in phr (parts per hundred parts of dry rubber) Experimentno. 1-1 1-2 1-3 1-4 1-5 1-6 1-7 1-8 1-9 Polymer 100 100 100 100 100 100100 100 100 Surfactant 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 KOH 1.7 1.71.7 1.7 1.7 1.7 1.7 1.7 1.7 Antioxidant 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.40.4 Tio2 3 3 3 3 3 3 3 3 3 Sodium 0.05 0.1 0.15 0.2 0.4 0.6 0.8 1.0 1.67aluminate NaOH 0.05 0.1 0.15 0.2 0.4 0.6 0.8 1.0 1.67 KOH 0.05 0.1 0.150.2 0.4 0.6 0.8 1.0 1.67 Glycerine 0.05 0.1 0.15 0.2 0.4 0.6 0.8 1.01.67

Polymer=commercially available carboxylated acrylonitrile butadienelatex—Nantex 6772

Surfactant=SDBS; Antioxidant is Lowinox CPL, a hindered phenolicantioxidant.

Sodium aluminate—the phr amounts refer to the total sodium aluminate.For corresponding phr amount of aluminium ions in solubilised form,multiply by 33%.

The properties of the films produced were tested and are set out in thetable below:

Consolidated Results of Physical Properties Accelerated Aging Unaged(100 deg. C./22 hrs) MMO Tensile M300 M500 Tensil M300 M500 Expt. (phr)(Mpa) EB % (Mpa) (Mpa) (Mpa) EB % (Mpa) (Mpa) 1-1 0.05 17.96 790 1.582.86 21.90 760 1.68 3.09 1-2 0.1 23.50 800 1.99 3.70 27.71 730 2.14 4.471-3 0.15 30.83 700 3.55 7.10 35.08 650 4.58 9.82 1-4 0.2 30.50 740 2.715.79 31.41 660 2.73 7.09 1-5 0.4 31.54 660 4.06 10.42 36.07 620 4.1512.78 1-6 0.6 28.97 540 6.18 22.53 37.55 550 9.31 30.55 1-7 0.8 31.40610 4.49 15.93 40.41 580 6.65 21.68 1-8 1 33.48 590 5.48 17.56 43.19 5509.98 32.99 1-9 1.67 31.64 540 8.19 23.65 35.57 560 10.35 30.06

Analysis of Results:

-   -   The use of solubilised sodium aluminate (providing an aqueous        solution of negatively charged aluminium hydroxide complex        ions), as the sole cross-linking agent, provides articles such        as films with good physical properties, even at lower phr        levels.

The before aging tensile strength values were between 18 MPa and 33.5MPa, and the after aging tensile strength values were between 22 MPa and43 MPa, with the increasing level of sodium aluminate, showing therelationship of direct proportionality to the quantity of sodiumaluminate. Considering the ASTM Standard Specification for Nitrilerubber examination gloves (ASTM D6319) minimum requirement of 14 MPa forexamination gloves, the glove will pass the strength criteriacomfortably even with the sodium aluminate level of less than 0.1 phr.

The above trend applies to M300 and M500 values too. At the lowest levelof 0.05 sodium aluminate the M300 is less than 2 MPa and M300 is lessthan 3 MPa. This indicates the gloves softness is close to the glovesmade out of natural rubber latex.

The before aging elongation at break is between 800% and 540% at unagedcondition and between 760% and 550% in the accelerated aging conditionat 100° C., for 22 hrs. Against the ASTM Standard Specification forNitrile rubber examination gloves (ASTM D6319) minimum requirement of500% unaged and 400% after accelerated aging, the gloves of Example 1surpass the requirements.

The above results imply the following:

a. The crosslinking density increases with the increasing dosage ofsolubilised negatively-charged multivalent metal complex ions, eventhough it is not truly linear, and the slope of the curve varies whencompared between tensile strength and elongation. In the case of unagedtensile strength, the increase is not so significant after 0.15 phr—thiscould be due to the limitation of available carboxylic group (—COOH).

b. The fact that such a high tensile could be achieved even with 0.15phr indicates that effective dissolution/ionization of the multivalentmetal (as a negatively-charged metal complex ion) enables best reactionpotential. Moreover, for trivalent metals such as aluminium, thetheoretical possibility of cross linking is 50% more than that ofdivalent metal ions. This makes a substantial impact. At lower level ofmultivalent metal the linear linkages are predominant and hence theelongation is high and modulus is low. At the higher level ofmultivalent metal, particularly a trivalent metal, the cross linkingbetween the linear chains are more and there is a higher occurrence ofthree dimensional cross linking resulting in lower elongation and highermodulus, although with a marginal loss of the soft elastomeric state asa consequence of the higher cross linking density. Of course, thisentire networking depends on the available carboxylic acid terminals andthe number of active ions.

c. This is achieved with lower cost, particularly in the example ofsodium aluminate as the source for the negatively charged multivalentmetal complex ions. The cost of sodium aluminate is around one thirdthat of solid-state ZnO. Together with the potential to use sodiumaluminate at a much lower dosage (by total weight of material, based ontypical ZnO usage levels), savings may be 10 to 20 fold.

d. At lower level of cross-linking agent (the multivalent metal incomplex ion form), the modulus at 300% is almost the same as naturalrubber, which imparts softness to the film even at low film thickness,or low film weight (e.g. for a glove having a weight of less than 4 gms(3.2 gm)). Such a low product weight will be possible with reasonableproduct endurance of 1-4 hrs of normal wearing conditions.

Through the use of a solubilised form of multivalent metal (i.e. throughthe formation of negatively charged complex of the multivalent metal),it is believed that the multivalent metal forms cross-links with

Comparative Example 2—Glyoxal or TMPTMA as the Sole Cross-Linking Agent

This comparative example was performed to evaluate films produced withalternative cross-linking agents of either the organic or inorganictype. Films were produced using the compositions shown below, whichcontained glyoxal or trimethylolpropane trimethacrylate multifunctionalmethacrylate polymer (TMPTMA) as the cross-linking agent, in place ofthe solubilised sodium aluminate. These films were produced inaccordance with steps 4-12 of the general procedure outlined above,following production of the latex composition in accordance with priorart practices.

Composition in phr (parts per hundred parts of dry rubber) Experimentno. 2-1 2-2 2-3 2-4 2-5 2-6 Polymer 100 100 100 100 100 100 Surfactant0.6 0.6 0.6 0.6 0.6 0.6 KOH 1.7 1.7 1.7 1.7 1.7 1.7 Antioxidant — — — —— — TiO2 3 3 3 3 3 3 Glyoxal 0.5 1.0 1.5 — — — TMPTMA — — — 0.5 0.1 1.5

Polymer=commercially available carboxylated acrylonitrile butadienelatex—Nantex 6772

Surfactant=50% SDBS and 50% SLES; Antioxidant is Lowinox CPL, a hinderedphenolic antioxidant.

Sodium aluminate—the phr amounts refer to the total sodium aluminate.For corresponding phr amount of aluminium ions in solubilised form,multiply by 33%.

The properties of the films produced were tested and are set out in thetable below:

Consolidated Results Glyoxal Unaged Aged-at 100 deg.C/22 hrs Expt. (phr)Tensile EB M300 M500 Tensile EB M300 M500 2-1 0.5 1.61 940 0.66 0.685.41 860 0.97 1.15 2-2 1.0 6.73 940 0.98 1.32 9.88 850 1.08 1.68 2-3 1.510.57 750 1.49 2.42 11.96 730 1.57 2.56 Consolidated Results TMPTMAUnaged Aged-at 100 deg.C/22 hrs Expt. (phr) Tensile EB M300 M500 TensileEB M300 M500 2-4 0.5 9.4 780 1.3 2.1 18.7 760 1.6 2.9 2-5 1.0 12.7 7801.4 2.4 16.9 740 1.8 3.3 2-6 1.5 8.2 780 1.1 1.8 15.5 740 1.5 2.8

Analysis of the Results:

These results assist to demonstrate the film properties as a baseline,so that combinations of other cross-linking agents with glyoxal orTMPTMA can be assessed. Glyoxal reacts with hydroxyl groups and formlinks however not as strongly as the ionic bonds created withmultivalent metals, thus leading to poor film formation. TMPTMA is a trifunctional reactive methacrylate monomer rendering covalent bond withthe base polymer.

Example 3—Combinations of Sodium Aluminate with Glyoxal or TMPTMA

This example was performed to evaluate the film behaviour usingsolubilised sodium aluminate together with an organic cross linker,providing covalent cross-linking. These films were produced inaccordance with the general procedure outlined above.

Composition in phr (parts per hundred parts of dry rubber) Experimentno. 3-1 3-2 3-3 3-4 Polymer 100 100 100 100 Surfactant 1.0 1.0 1.0 1.0KOH 1.8 1.8 1.8 1.8 Antioxidant 0.5 0.5 0.5 0.5 TiO2 3 3 3 3 Sodiumaluminate 0.1 0.1 0.2 0.2 NaOH 0.1 0.1 0.2 0.2 KOH 0.1 0.1 0.2 0.2Glycerine 0.1 0.1 0.2 0.2 Glyoxal 0.5 1.0 1.5 2.0 TMPTMA 0.5 1.0 1.5 2.0

Polymer=commercially available carboxylated acrylonitrile butadienelatex—Nantex 6772

Surfactant=50% SDBS and 50% SLES; Antioxidant is Lowinox CPL, a hinderedphenolic antioxidant.

Sodium aluminate—the phr amounts refer to the total sodium aluminate.For corresponding phr amount of aluminium ions in solubilised form,multiply by 33%.

The properties of the films produced were tested and are set out in thetable below:

Consolidated Results Unaged Aged-at 100 deg.C/22 hrs Expt. Tensile EBM300 M500 Tensile EB M300 M500 3-1 15.4 777 1.4 2.5 17.7 715 1.8 3.7(0.1,0.5,0.5) 3-2 19.9 767 1.8 3.4 25.8 720 2.1 4.5 (0.1,1,1) 3-3 23.6720 2.2 4.9 30.9 693 2.7 6.6 (0.2,1.5,1.5) 3-4 21.0 740 2.1 4.6 27.8 7202.4 5.7 (0.2,2,2)

Analysis of the Results:

Following completion of Example 1, it was postulated that the additionof an organic cross-linking agent would improve the film properties. Itwas postulated that an organic cross linker would provide covalent bondswhich would improve the elastic properties and water resistanceproperties of the film. The covalent bond acts like a micro spring toenable comparably better elasticity and sustaining of the same.

This example involved the preparation of four sets of experiments: twocontaining 0.1 phr of sodium aluminate, and two containing 0.2 phrsodium aluminate. Comparing the results obtained to those in Example 1,the following observations were made:

a. In Example 1, it was observed that increasing the amount of sodiumaluminate (i.e. the amount of solubilised aluminium) increases thetensile strength and the modulus and reduces the elongation.

b. The additional inclusion of an organic cross linker in this zone of0.1 phr sodium aluminate does not significantly change the filmproperties obtained—this may be attributed to insufficient ionicbonding. Another possible explanation is that the film formation starvesthe opportunity to obtain optimal completion of ionic bonding.

c. As seen in Example 1, where only sodium aluminate is used as thecross-linking agent, an optimum reached between 0.15 to 0.2 phr ofsodium aluminate (noting that this corresponds to about 0.05-0.67 phraluminium ions). As a consequence, experiments 3-3 and 3-4 were selectedat the sodium aluminate level of 0.2 phr.

d. For 3-3 and 3-4, which are based on the same amount of sodiumaluminate, the increase in the amount of organic cross-linker in theformulation reduces the modulus and increases the elongation. The glovestoo felt relatively soft and silky touch—perceived to be less creased.

e. Comparing Example 3-4 to Example 1-4, each of which contains the sameamount of sodium aluminate, there is a reduction in the Modulus at 300%and 500% from 2.71 to 2.1 and 5.79 to 4.6 respectively. In the case ofan aged sample, the M300% and M500% drops are from 2.73 to 2.4 and 7.1to 5.7 respectively. This supports the inference in point d.

f. Further to the above point, the unaged modulus remains the same,however the aged elongation at break increases when adding the organiccross-linker (i.e. comparing 3-4 to Example 1-4), from 660% to 720%.

Example 4—Combination of Sodium Aluminate with a Sulphur-BasedCross-Linker

This example was performed to understand the influence of sulphur andsulphur-donor cross-linkers on films also containing solubilised sodiumaluminate. Three different sulphur donors were selected—ZDBC, ZDMC andDPTT. These films were produced in accordance with the general procedureoutlined above.

Composition in phr (parts per hundred parts of dry rubber) Experimentno. 4-1 4-2 4-3 4-4 4-5 Polymer 100 100 100 100 100 SDBS Surfactant 0.50.5 0.5 1.0 0.5 SLES Surfactant 0.5 0.5 — — — KOH 1.8 1.7 1.7 1.8 1.7Antioxidant 0.5 0.5 0.5 0.5 0.5 TiO2 3 3 3 3 — Sulphur 1 0.25 0.25 1 0.5ZDMC — 0.25 — — — DPTT — — 0.25 — 0.5 ZDBC 0.25 — — 0.2 — Sodiumaluminate 0.05 0.05 0.05 0.1 0.15 NaOH 0.05 0.05 0.05 0.1 0.15 KOH 0.050.05 0.05 0.1 0.15 Glycerine 0.05 0.05 0.05 0.1 0.15 Glyoxal — 1 1 1 1

Polymer=commercially available carboxylated acrylonitrile butadienelatex—Nantex 6772

Antioxidant is Lowinox CPL, a hindered phenolic antioxidant.

The properties of the films produced were tested and are set out in thetable below. For convenient comparison, parts of the table of resultsfor Example 1 are also shown in the second table below:

Consolidated Results Unaged Aged-at 100 deg.C/22 hrs Expt. Tensile EBM300 M500 Tensile EB M300 M500 4-1 23.61 740 2 4.16 26.23 680 2.37 5.654-2 17.09 730 1.81 3.51 17.69 680 1.96 4.27 4-3 12.88 790 1.35 2.2713.60 780 1.54 2.67 4-4 16.41 740 1.35 2.30 17.69 730 1.81 3.61 4-519.53 730 1.71 3.44 30.97 720 2.36 5.95

Results Sodium From aluminate Unaged Aged Expt. 1 Level Tensile EB M300M500 Tensile EB M300 M500 1-1 0.05 17.96 790 1.58 2.86 21.90 760 1.683.09 1-2 0.10 23.50 800 1.99 3.70 27.71 730 2.14 4.47 1-3 0.15 30.83 7003.55 7.10 35.08 650 4.58 9.82

Tensile, M300 & M500 are in mPa; Elongation at break in percentage.

Analysis of the Results:

It is useful to compare 4-1, 4-2 and 4-3 with Example 1-1 (whichcontains the same level of sodium aluminate), 4-4 with Example 1-2, and4-5 with Example 1-3.

a. In Example 1-1, the sodium aluminate amount of 0.05 phr aloneprovided a tensile strength of about 18 MPa. The addition of sulphur inan amount of 1 phr and ZDBC in an amount of 0.25 phr only provided anadditional tensile strength of about 5 MPa—this indicates that thesolubilised sodium aluminate provides the maximum strength with theminimal dosage of 0.05 phr which is equivalent to 1/25 (on a weightbasis) of the combined amount of sulphur and sulphur donors.

b. On an overall basis the unaged elongation is more than 730% in allthe experiments and in 4-3 it reached up to 790% (where DPTT is used).

c. In the case of after-aging elongation, the values ranges from 680% to780% (DPTT).

d. In the case of un-aged M300 values except CS1, all the un-aged valuesare less than 2 MPa, which is an indication of the softness of the film.

e. In the case of aged M300 values, 4-2, 4-3 and 4-4 were found to havevalues less than 2 MPa.

f. In the case of un-aged M500 values, four of the readings were below4, and two were below 3 MPa.

g. In the case of aged M500 values, three products had values less than5, two products had values less than 4, and one product had a value lessthan 3.

h. When the amount of solubilised sodium aluminate at the lowest amounttested of 0.05, the higher amount of sulphur (in presence of ZDBC)increased the strength of the film.

i. As shown previously above, the optimum ionic cross linking is reachedat 0.15 phr of sodium aluminate (i.e. 0.05 phr aluminium). It is usefultherefore to compare the results obtained in Example 1-3 (0.15 phrsodium aluminate) and Example 4-5 (containing 0.15 phr sodium aluminateand sulphur). The modulus values of both M300 and M500 is substantiallyreduced by the addition of the sulphur (and DPTT) for both unaged andaged conditions. The elongation of Example 4-5 is higher than that ofExample 1-3 in both unaged and aged conditions. This is desirable.

j. Similarly, the modulus values obtained in Example 4-4 are moredesirable than those obtained in Example 1-2. The modulus values of bothM300 and M500 substantially reduces in the case of sulphur addition, forboth unaged and aged conditions.

k. Hence it can be deduced that where lower modulus values are desired,covalent bonding through sulphur and sulphur donor addition to theformulation is effective.

For gloves, the presence of both of ionic cross-links (particularly ascan be achieved with the solubilised negatively-charged multivalentmetal complex ion-containing cross-linking agent) and covalentcrosslinking mechanism is desirable in the formation of products such asgloves.

Example 5—Other Sources of Cross-Linking Agent

Films were produced using the compositions shown below, each containingsolubilised aluminium. This example was performed to demonstrate theproduction of films using different sources for the cross-linkingagent—that is, through replacing the sodium aluminate with alum(potassium aluminium sulphate), PAC (poly aluminium chloride) and PFS(poly ferric sulphate), and to enable evaluation of the films produced.The films were produced in accordance with the general procedureoutlined above, including all of steps 1 to 12.

Composition in phr (parts per hundred parts of dry rubber) Experimentno. 5-1 5-2 5-3 5-4 5-5 5-6 5-7 5-8 5-9 5-10 Polymer 100 100 100 100 100100 100 100 100 100 SDBS Surfact't 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.40.4 KOH 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 1.8 Antioxidant 0.4 0.4 0.40.4 0.4 0.4 0.4 0.4 0.4 0.4 Tio2 3 3 3 3 3 3 3 3 3 3 ALUM X-Link 0.6750.338 0.169 0.084 — — — — — — PAC X-Link — — — — 0.930 0.465 0.233 0.116— — PFS X-Link — — — — — — — — 0.75 0.5

Polymer=commercially available carboxylated acrylonitrile butadienelatex—Nantex 6772

Antioxidant is Lowinox CPL, a hindered phenolic antioxidant.

ALUM X-Link, PAC X-Link and PFS X-Link is a short-hand reference to thecompositions set out in the table that follows immediately below. Thephr amounts in the above table refer to the phr amounts of the ALUM, PACand PFS (alone). As shown in the table below, the relevant X-Linkercontained additional components.

Cross linking composition Composition in phr Experiment Salt Salt NaOHKOH Glycerine SDBS 5-1 Alum 0.675 1.35 0.675 0.675 0.6 5-2 Alum 0.3381.35 0.675 0.675 0.6 5-3 Alum 0.169 1.35 0.675 0.675 0.6 5-4 Alum 0.0841.35 0.675 0.675 0.6 5-5 PAC 0.930 0.93 0.75 0.75 0.6 5-6 PAC 0.465 0.930.75 0.75 0.6 5-7 PAC 0.233 0.93 0.75 0.75 0.6 5-8 PAC 0.116 0.93 0.750.75 0.6 5-9 PFS 0.75 3 0.675 0.675 0.6 5-10 PFS 0.5 3 0.675 0.675 0.6

The properties of the films produced were tested and are set out in thetable below.

Trivalent UNAGED AGED Expt Salt phr Tensile EB M300 M500 Tensile EB M300M500 Alum 5-1 0.675 27.46 610 3.51 10.68 34.02 700 3.23 7.02 5-2 0.33828.45 610 3.98 10.7 32.09 630 3.41 9.94 5-3 0.169 31.79 640 3.16 8.7436.79 650 3.21 8.05 5-4 0.084 40.38 640 3.9 11.86 37.64 600 3.96 16.53Poly Aluminium Chloride phr 5-5 0.930 33.78 620 3.15 10.29 38.07 6204.01 13.15 5-6 0.465 34.26 610 4.31 13.67 36.32 630 3.59 10.3 5-7 0.23334.23 620 3.82 10.76 22.54 690 2.28 4.9 5-8 0.116 32.08 600 3.93 12.9637.77 620 4.01 13.52 Poly Ferric Sulphate phr 5-9 0.75 31.14 580 5.1719.12 18.7 640 2.63 5.75 5-10 0.5 28.36 600 3.67 11.73 36.45 630 4.0312.71

Analysis of the Results:

The results of Example 5 demonstrate that it is possible to produceproducts from latex compositions containing cross-linking compositionsbased on sources of multivalent metals other than sodium aluminate—thesalt forms in particular. Films were produced from the latexcompositions containing ionic cross-linking based on the metals presentin the cross-linking compositions. The alum and PAC were able to formclear solutions of the cross-linking agent. The properties of the filmsproduced did not follow the typical pattern shown in earlier examples ofincreasing tensile strength with increasing cross-linking agent amounts.This suggests that the additional ions present in the compositions maybe influencing the cross-linking. Further modifications to thecompositions are expected to result in improvements to the filmsproduced in these examples.

Example 6—Sodium Aluminate with Added Solid Metal Oxide Cross-LinkingAgents

This example was performed to explore the properties of films containingsolubilised negatively-charged aluminium hydroxide complex ions,distributed evenly throughout the product, together with traditionalsolid ionic cross-linking agent, which will be concentrated around theparticles in the final product. These films were produced in accordancewith the general procedure outlined above, with the sodium aluminatebeing solubilised prior to addition to the polymer suspension, and lateraddition of the metal oxide as one of the finely milled solidcomponents. The input components were as outlined in the followingtable:

Composition in phr parts per hundred parts of dry rubber) Experiment No6-1 6-2 6-3 6-4 6-5 6-6 6-7 6-8 Polymer 100 100 100 100 100 100 100 100KOH 1.7 1.7 1.7 1.7 1.7 1.7 1.7 1.7 SDBS-Surfactant 0.3 0.3 0.3 0.3 0.30.3 0.3 0.3 SLES-Surfactant 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 Antioxidant0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 TiO2 3 3 3 3 3 3 3 3 Sodium aluminate0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 NaOH 0.15 0.15 0.15 0.15 0.150.15 0.15 0.15 KOH 0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Glycerine0.15 0.15 0.15 0.15 0.15 0.15 0.15 0.15 Zinc Oxide 0.05 0.1 0.15 0.2Magnesium Oxide 0.05 0.1 0.15 0.2 Composition in phr (parts per hundredparts of dry rubber) Experiment No 6-9 6-10 6-11 6-12 6-13 6-14 Polymer100 100 100 100 100 100 KOH 1.7 1.7 1.7 1.7 1.7 1.7 SDBS-Surfactant 0.30.3 0.3 0.3 0.3 0.3 SLES-Surfactant 0.3 0.3 0.3 0.3 0.3 0.3 Antioxidant0.4 0.4 0.4 0.4 0.4 0.4 TiO2 3 3 3 3 3 3 Sodium aluminate 0.075 0.0750.075 0.075 0.075 0.075 NaOH 0.075 0.075 0.075 0.075 0.075 0.075 KOH0.075 0.075 0.075 0.075 0.075 0.075 Glycerine 0.075 0.075 0.075 0.0750.075 0.075 Zinc Oxide 0.025 0.05 0.075 0.1 0 0 Magnesium Oxide 0.050.025 0 0 0.075 0.1

Polymer=commercially available carboxylated acrylonitrile butadienelatex—Nantex 6772

Antioxidant is Lowinox CPL, a hindered phenolic antioxidant.

The properties of the films produced were tested and are set out in thetable below.

UNAGED AGED Experiment No Tensile EB M300 M500 Tensile EB M300 M500 6-126.01 680 2.71 6.6 26.72 680 2.89 6.62 6-2 23.94 670 2.53 6.31 25.45 6702.2 4.76 6-3 29.91 670 3.01 7.5 27.61 650 2.46 6.4 6-4 29.16 650 3.027.75 35.36 650 3.53 8.9 6-5 22.29 690 2.25 4.6 25.49 660 2.47 5.95 6-623.27 680 2.29 5.26 26.21 650 2.49 6.11 6-7 18.81 690 2.01 3.99 22.78650 2.21 5.22 6-8 20.76 740 1.85 3.47 22.79 690 1.9 3.96 6-9 20.1 7401.87 3.67 19.26 670 2.06 4.25 6-10 20.46 730 1.92 3.76 23.42 660 2.35.35 6-11 16.72 740 1.69 3.37 21.87 650 2.09 4.4 6-12 23.68 710 2.194.36 26.8 680 2.62 6.13 6-13 20.76 690 1.85 3.87 24.16 720 2.5 5.15 6-1423.68 710 2.19 4.36 19.63 690 2.27 4.53

Analysis of Results:

The results obtained show that there is a slight improvement to the filmthrough the addition of a second cross-linker, comprising a solid metaloxide. The film formation (uniform film formation) is good when a smallquantity of ZnO or MgO is added.

Comparative Example 7—ZnO as Sole Ionic Cross-Linking Agent

This example was performed to explore the properties of films containingsolid zinc oxide as the cross-linking agent, to enable a comparison tobe made against a film containing solubilised metal (in the form ofnegatively charged aluminium hydroxide complex ions). These films wereproduced in accordance with the general procedure outlined above,although without the use of the cross-linking composition of theinvention. Instead, the metal oxide was added at the time indicated forthat component in the general procedure. The input components were asoutlined in the following tables:

7-1 7-2 7-3 7-4 7-5 7-6 7-7 7-8 7-9 7-10 7-11 7-12 NBR latex 100 100 100100 100 100 100 100 100 90 90 90 Chloroprene — — — — — — — — — 10 10 10latex KOH 0.5 0.5 — 0.5 0.5 — 0.5 0.5 — 0.5 0.5 — SDBS- 0.3 — 0.5 0.3 —0.5 0.3 — 0.5 0.3 — 0.5 Surfactant Solid Zinc 1.2 1.2 1.2 0.6 0.6 0.6 22 2 2.4 2.4 2.4 oxide Anti oxidant 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.50.5 0.5 0.5 Calcium — — — 5 5 5 5 5 5 5 5 5 carbonate Potassium 1 1 1 11 1 1 1 1 1 1 1 stearate

The antioxidant was Lowinox CPL.

The properties of the films produced were tested and are set out in thetables below.

Consolidated Results-Part 1/4 7-1 7-2 7-3 Aged Aged Aged Aged Aged Aged70 100 70 100 70 100 degC degC degC degC degC degC Property Unaged 7days 1 day Unaged 7 days 1 day Unaged 7 days 1 day Tensile 15.2 16.718.9 22.2 24.03 18.8 15.6 9.45 15.93 (Mpa) M300 1.6 1.8 2.3 2.1 1.891.97 1.7 1.3 1.69 (Mpa) M500 2.9 3.6 4.9 4 3.68 4.09 2.8 1.91 3.02 (Mpa)EB (%) 727 700 660 727 733 687 753 753 707 pH 8.7 8.9 8.2

Consolidated Results-Part 2/4 7-4 7-5 7-6 Aged Aged Aged Aged Aged Aged70 100 70 100 70 100 degC degC degC degC degC degC Property Unaged 7days 1 day Unaged 7 days 1 day Unaged 7 days 1 day Tensile 21.2 29.530.51 29.7 34.14 25.25 23.1 14.07 20.13 (Mpa) M300 1.9 2.1 2.9 2.7 2.542.34 2 1.5 2.13 (Mpa) M500 3.4 4.6 6.8 5.4 5.23 4.59 3.6 2.23 3.74 (Mpa)EB (%) 753 720 667 707 727 707 753 767 713 pH 8.7 8.8 8.1

Consolidated Results-Part 3/4 7-7 7-8 7-9 Aged Aged Aged Aged Aged Aged70 100 70 100 70 100 degC degC degC degC degC degC Property Unaged 7days 1 day Unaged 7 days 1 day Unaged 7 days 1 day Tensile 31.1 27.243.5 46.7 44.94 49.99 30.41 32.35 36.97 (Mpa) M300 5.3 2.9 6.2 8 6.756.76 5 4.13 5.51 (Mpa) M500 16.6 6.4 19.4 30 22.48 25.36 17.6 12.7319.78 (Mpa) EB (%) 593 687 620 560 607 600 567 613 580 pH 8.7 8.8 8.2

Consolidated Results-Part 4/4 7-10 7-11 7-12 Aged Aged Aged Aged AgedAged 70 100 70 100 70 100 degC degC degC degC degC degC Property Unaged7 days 1 day Unaged 7 days 1 day Unaged 7 days 1 day UTS (Mpa) 27.2 38.638.3 34.2 38.05 39.07 35.95 39.11 37.47 M300 (Mpa) 5.4 6.1 5.9 7.9 5.395.87 7.7 4.97 5.36 M500 (Mpa) 16.2 21.4 17.1 24.9 15.93 17.51 24.7 16.4218.35 EB (%) 580 587 633 553 627 620 540 613 607 pH 9.1 9.4 8.6

As stated above, examples 7-1 to 7-12 represent the use of theconventional solid zinc oxide cross-linker. The examples were performedwithout sulphur or other covalent cross-linking agent. The amount of ZnOused in the examples was between 0.6 and 2.4. The elongation and modulusvalues obtained from testing the products of this example were inferiorto those of Example 1, and were reflected in poor user comfort levels.

Example 8—Double-Layer Gloves Formed Using Sodium Aluminate, Sulphur anda Sulphur Donor as the Sole Cross-Linking Agents, in Each Layer

This example was performed to demonstrate commercial scale production ofgloves (in different sizes) containing solubilised sodium aluminatecross-linker, together with sulphur and sulphur-donor cross-linkers assecondary cross-linkers. These films were produced in accordance withthe general procedure outlined above, with the modification that thesecond dipping step was based on a different composition compared to thefirst dipping composition. The gloves were double tone (blue and white),300 mm long, and had an average weight (for medium size) of 9.5 grams.

The composition for the 1^(st) layer—the working side, was as follows(in phr):

White Compound Nantex 6772 100 KOH 1.0 Sodium aluminate 0.1 SULPHUR 0.6ZDBC 0.4 ANTIOXIDANT 0.4 TiO₂ 6.0 Calcium Carbonate 2.0

The composition for the 2^(nd) layer—the donning side, was as follows(in phr):

Cobalt Blue Compound Nantex 6772 100 KOH 1.0 sodium aluminate 0.1SULPHUR 0.6 ZDBC 0.4 ANTIOXIDANT 0.4 TiO₂ 6.0 VIOLET BLUE 0.5 MPL15660.14 MPL1857 B 0.7

A) Dimensions and Physical Properties:

DIMENSION Size Thickness (and sample Weight Length Width Cuff PalmFinger number) (gram) (mm) (mm) (mm) M 8.1 9.56 301 97 0.12 0.13 0.188.2 9.44 304 99 0.11 0.14 0.17 8.3 9.72 304 99 0.12 0.14 0.18 8.4 9.83302 99 0.13 0.14 0.17 8.5 9.63 302 99 0.13 0.14 0.17 8.6 9.72 301 990.13 0.14 0.16 8.7 9.46 301 98 0.13 0.14 0.20 8.8 9.89 302 99 0.15 0.130.17 8.9 9.56 300 99 0.12 0.13 0.17 8.10 9.74 301 99 0.13 0.14 0.17Average 9.66 302 99 0.13 0.14 0.17

PHYSICAL PROPERTIES Size UNAGED (and sample Tensile Elongation Mod@300Mod@500 Load Break number) (Mpa) (%) (Mpa) (Mpa) (N) M 8.1 16.55 7801.77 2.91 10.78 8.2 18.13 760 1.86 3.32 10.50 8.3 17.54 760 1.80 3.1210.56 8.4 18.51 760 1.90 3.33 10.23 8.5 17.87 780 1.73 2.92 10.47 8.617.90 760 1.82 3.29 11.10 8.7 8.8 8.9 8.10 Average 17.75 767 1.81 3.1510.53

PHYSICAL PROPERTIES Size AGED (and sample Tensile Elongation Mod@300Mod@500 Load Break number) (Mpa) (%) (Mpa) (Mpa) (N) M 8.1 24.92 7402.32 4.56 12.83 8.2 19.99 720 2.25 4.20 10.40 8.3 27.92 740 2.47 4.5712.79 8.4 25.02 740 2.41 4.77 12.26 8.5 20.84 720 2.42 4.72 12.56 8.624.80 760 2.24 4.33 12.02 8.7 8.8 8.9 8.10 Average 23.92 737 2.35 4.5312.41

DIMENSION Size Thickness (and sample Weight Length Width Cuff PalmFinger number) (gram) (mm) (mm) (mm) L 8.1 10.76 305 109 0.11 0.14 0.168.2 10.76 302 110 0.11 0.13 0.18 8.3 10.76 304 110 0.12 0.14 0.18 8.411.00 301 110 0.13 0.13 0.16 8.5 11.11 302 111 0.13 0.14 0.19 8.6 10.26302 109 0.11 0.13 0.16 8.7 10.48 303 110 0.11 0.13 0.16 8.8 10.17 302109 0.11 0.12 0.16 8.9 9.80 300 110 0.11 0.13 0.17 8.10 10.68 303 1100.11 0.13 0.18 Average 10.58 302 110 0.12 0.13 0.17

PHYSICAL PROPERTIES Size UNAGED (and sample Tensile Elongation Mod@300Mod@500 Load Break number) (Mpa) (%) (Mpa) (Mpa) (N) L 8.1 17.72 800.001.60 2.70 10.50 8.2 21.02 820.00 1.72 2.86 10.15 8.3 19.10 800.00 1.552.72 11.10 8.4 20.97 820.00 1.81 3.00 9.65 8.5 20.32 800.00 1.78 3.068.92 8.6 20.90 800.00 1.85 3.12 9.92 8.7 8.8 8.9 8.10 Average 20.01 8071.72 2.91 10.04

DIMENSION Size Thickness (and sample Weight Length Width Cuff PalmFinger number) (gram) (mm) (mm) (mm) XL 8.1 11.29 307 119 0.11 0.13 0.168.2 11.89 303 120 0.12 0.14 0.19 8.3 11.85 300 119 0.12 0.13 0.19 8.411.71 302 120 0.13 0.14 0.16 8.5 11.87 302 119 0.13 0.14 0.18 8.6 11.97303 120 0.13 0.14 0.18 8.7 11.69 301 119 0.12 0.14 0.17 8.8 11.48 301120 0.12 0.13 0.18 8.9 11.89 301 119 0.12 0.14 0.19 8.10 11.58 300 1200.13 0.14 0.17 Average 11.72 302 120 0.12 0.14 0.18

PHYSICAL PROPERTIES Size UNAGED (and sample Tensile Elongation Mod@300Mod@500 Load Break number) (Mpa) (%) (Mpa) (Mpa) (N) XL 8.1 17.19 800.001.58 2.58 10.50 8.2 20.01 800.00 1.85 3.09 10.01 8.3 18.93 780.00 1.783.03 12.12 8.4 18.99 800.00 1.69 2.91 9.94 8.5 18.56 780.00 1.89 3.2710.87 8.6 17.92 780.00 1.65 2.77 9.38 8.7 8.8 8.9 8.10 Average 18.60790.00 1.74 2.94 10.47B) Overall Physical Properties for M size

PHYSICAL PROPERTIES UNAGED Tensile Elongation Mod@300 Mod@500 Load Break(Mpa) (%) (Mpa) (Mpa) (N) 20.46 760 2.04 3.59 9.55 19.96 760 1.86 3.289.81 20.21 760 1.95 3.44 9.68

PHYSICAL PROPERTIES AGED Tensile Elongation Mod@300 Mod@500 Load Break(Mpa) (%) (Mpa) (Mpa) (N) 25.30 740 2.30 4.74 13.94 25.66 720 2.47 5.1110.71 25.48 730 2.39 4.93 12.33

Example 9—Second Cross-Linking Agent Comprising Sulphur and SulphurDonor

This example demonstrates the results obtained when using sulphur andsulphur-donor cross-linkers as the second cross-linking agents (the onlysecondary cross-linking agents) in addition to sodium aluminate as theprimary cross-linking agent. These films were produced in accordancewith the general procedure outlined above. The films produced were inthe form of gloves with an average thickness of about 0.05-0.10 mm—lessthan 0.2 mm.

Composition in phr Example 9-1 Example 9-2 Nantex 6772 100 100 KOH 1 1Surfactant - Agwet 0.6 0.6 Sodium Aluminate 0.08 0.12 NaOH 0.08 0.12 KOH0.08 0.12 Glycerine 0.08 0.12 Sulphur 0.6 — DPTT 0.2 0.3 ZDBC 0.2 0.3TiO2 2.5 2.5 Antioxidant 0.4 0.4

Agwet is a sodium salt of dodecyl benzene sulfonate.

The antioxidant is Lowinox CPL, a hindered phenolic antioxidant.

The properties of the films produced were tested and are set out in thetable below. It is noted that EN refers to Force at Break measured inaccordance with the European Norms—the European standard EN 455-2, andis measured in Newtons.

UNAGED Weight Tensile EB M300 M500 EN Compound (gm) (Mpa) (%) (Mpa)(Mpa) (N) Ex. 9-1 4.3 14.77 820 1.42 2.2 4.8 Ex. 9-2 4.2 17.92 760 1.612.79 5.35

AGED (100 deg. C./22 hrs) EN Compound Weight Tensile EB M300 M500 (N)Ex. 9-1 4.3 20.94 740 1.98 3.59 6.63 Ex. 9-2 4.2 24.91 750 2.22 4.127.59

Analysis of the Results:

The results of Example 9 demonstrate the production of articles (gloves)having excellent properties, produced using sodium aluminate in anamount of well below 0.3 phr, in combination with either sulphur andsulphur-donor crosslinking agents, or sulphur-donor cross-linking agentswithout sulphur, to the exclusion of any other cross-linking agents.Comparing Example 9-1 to Example 9-2, the lower level of sodiumaluminate results in lower tensile strength and higher elongation (seeExample 9-1). The converse (Example 9-2) results in higher tensilestrength and lower elongation. The M500 values are less than 3 beforeaging and less than 5 after accelerated aging—both well below 6.5, for aglove thickness of less than 0.2 mm. The product produced with sulphurand/or a sulphur donor can achieve engloation higher than 800% prior toaging, and still as high as 750% after aging. Comparing the results inExample 9 to those of Example 4, Examples 4-2 to 4-5 contain glyoxal asan additional cross-linker. Example 9-1 contains no glyoxal and containssulphur and a sulphur donor, and Example 9-2 contains just a sulphurdonor (without sulphur), in addition to the solubilised sodium aluminatecross-linking agent. In Example 9, high elongation, above 700%, isachieved with the selected cross-linking agents.

Example 10—Second Cross-Linking Agent Comprising Metal Oxide as the SoleSecondary Cross-Linking Agent

This example demonstrates the results obtained when using (solid) metaloxide cross-linking agent(s) as the second cross-linking agent(s) (i.e.the only secondary cross-linking agents) in addition to sodium aluminateas the primary cross-linking agent. These films were produced inaccordance with the general procedure outlined above. The films producedwere in the form of gloves with an average thickness of about 0.05-0.10mm—less than 0.2 mm.

Components in phr Ex. 10-1 Ex. 10-2 Nantex 6772 100 100 KOH 1 1Surfactant - Agwet 0.6 0.6 Sodium Aluminate 0.1 0.05 NaOH 0.1 0.05 KOH0.1 0.05 Glycerine 0.1 0.05 Zink Oxide 0.2 0.2 Magnesium Oxide — 0.3TiO2 2.5 2.5 Antioxidant 0.4 0.4

Agwet is a sodium salt of dodecyl benzene sulfonate.

The antioxidant is Lowinox CPL, a hindered phenolic antioxidant.

The properties of the films produced were tested and are set out in thetable below. The units of measurement are the same as presented in thetables for Example 9.

UNAGED Compound Weight Tensile EB M300 M500 EN Ex. 10-1 4.2 22.96 7602.03 3.98 5.4 Ex. 10-2 4.2 18.41 740 1.8 3.27 6.39

AGED (100 deg. C./22 hrs) Compound Weight Tensile EB M300 M500 EN Ex.10-1 4.2 24.07 720 2.23 4.34 6.3 Ex. 10-2 4.2 21.94 720 2.11 3.93 7.41

Analysis of the Results:

The results of Example 10 demonstrate the production of articles(gloves) having excellent properties, produced using sodium aluminate inan amount of well below 0.3 phr, in combination with either zinc oxideor a combination of metal oxides (zinc and magnesium oxide), to theexclusion of any other cross-linking agents. Comparing Example 10-1 toExample 10-2, there is a reduction in the amount of sodium aluminate by0.05 phr, which is substituted with 0.3 phr magnesium oxide. Even withan addition of 0.3 phr of MgO, this could not compensate for thereduction in 0.05 phr amount of sodium aluminate, in solubilised form,demonstrating again the unexpectedly high effectiveness of this reagenton a weight-for-weight basis with other possible cross-linking agents,especially considering the comparison in the tensile values obtained,where the MgO in product of Example 10-2 failed to fully compensate forthe reduction in sodium aluminate. The lower level of sodium aluminatein Example 10-2 results in lower tensile and higher elongation comparedto the results in Example 10-1. The M500 results are less than 4.0before aging and less than 5.0 after aging, and well below 6.5 in eachcase. The elongation is at least 720% in both the aged and unagedcondition, and higher than 750 in one case in the unaged condition.

The results of Example 10 provide an improvement upon the results shownin Example 6, and guide the selection of components suitable forcommercial production of gloves based on a combination of solubilisedsodium aluminate and metal oxide. The amounts selected follow extensivetesting and optimisation, with a focus on amounts of around 0.01-0.6 phr(suitably 0.01-0.4 phr) metal oxide, and 0.01-0.2 phr sodium aluminate.Example 10-1 is preferred over Example 10-2.

Example 11—Second Cross-Linking Agent Comprising Sulphur, One or MoreSulphur Donors, and One or More Metal Oxides as the Only SecondaryCross-Linking Agents

This example demonstrates the results obtained when using sulphur,sulphur donor(s) and metal cross-linking agent(s) as the secondcross-linking agent(s) (i.e. the only secondary cross-linking agents) inaddition to sodium aluminate (or other dissolved multivalent metaloxide, hydroxide or salt) as the primary cross-linking agent. Thesefilms were produced in accordance with the general procedure outlinedabove. The films produced were in the form of gloves with an averagethickness of about 0.05-0.10 mm—less than 0.2 mm.

Components in phr Ex. 11-1 Ex 11-2 Nantex 6772 100 100 KOH 1 1Surfactant - Agwet 0.6 0.6 Sodium Aluminate 0.08 0.1 NaOH 0.08 0.1 KOH0.08 0.1 Glycerine 0.08 0.1 Sulphur 0.3 0.2 DPTT 0.1 0.1 ZDBC 0.1 0.05Zinc Oxide 0.1 0.1 Magnesium Oxide 0.2 0.3 TiO2 2.5 2.5 Antioxidant 0.40.4

Agwet is a sodium salt of dodecyl benzene sulfonate.

The antioxidant is Lowinox CPL, a hindered phenolic antioxidant.

The properties of the films produced were tested and are set out in thetable below. The units of measurement are the same as presented in thetables for Example 9.

UNAGED Compound Weight Tensile EB M300 M500 EN Ex. 11-1 4.2 26.29 7502.07 3.99 5.89 Ex. 11-2 4.3 24.61 740 2.24 4.22 6.23

AGED (100 deg. C./22 hrs) Compound Weight Tensile EB M300 M500 EN Ex.11-1 4.2 27.28 700 2.18 4.65 7.5 Ex. 11-2 4.3 34.43 690 2.36 5.8 7.79

Analysis of the Results:

The results of Example 11 demonstrate the production of articles(gloves) having excellent properties, produced using sodium aluminate(or other dissolved multivalent metal oxide, hydroxide or salt) in anamount of well below 0.3 phr, in combination with sulphur, sulphurdonor(s) and metal cross-linking agent(s) as the second cross-linkingagent(s) (i.e. the only secondary cross-linking agents). Between the twotrials, the amount of sodium aluminate differed by 0.02 phr. However,the most influencing factor was found to be sulphur and thesulphur-donor ZDBC for the before-aging results. In the case of thepost-aged product, the tensile values of Example 11-2 increasedconsiderably. While there can be variation in the individual glovesproduced in accordance with these compositions, based on average valuescalculated from a sample of at least 10 gloves, the amounts ofcomponents indicated in this Example have been selected for theirsuitability for commercial products based on the given combination ofcross-linking agents.

Comparative Example 12—Unsuccessful Trials

Several trials were performed prior to identifying the new compositionsand methods of the invention to try to incorporate multivalent metalsinto synthetic polymers in new and effective ways. The techniquesattempted included:

-   -   Adding aluminium oxide in solid form to an aqueous suspension of        carboxylated synthetic rubber (Nantex 6772). Poor film        properties were obtained, with respect to strength, modulus,        elongation, softness and feel, for additions up to 5 phr. Based        on the understanding since developed, it is understood that when        added in a solid form without solubilisation, the        aluminium-based cross-linking agent is not as effective.

The agent is not sufficiently available for cross-linking with thecarbon/late groups.

-   -   Attempting to dissolve zinc oxide in solution for addition in a        solubilised form. The techniques attempted to solubilise the        zinc oxide were not effective. The unsuccessful techniques        included adding sodium hydroxide and heating. To achieve the        formation of zinc-based negatively-charged complex ions, a        different source of zinc is required and/or different        solubilising conditions.    -   Adding sodium aluminate directly to an aqueous suspension of        carboxlated synthetic rubber emulsion (NANTEX 6772). This        resulted in micro-coagulam (i.e. localised immediate        cross-linking), and even gelling of the entire emulsion.    -   Forming a simple solution of sodium aluminate, and storing prior        to usage. When added to an aqueous suspension of carboxylated        synthetic rubber emulsion, micro-coagulam was created. It was        concluded that that the sodium aluminate had recrystallized upon        storage. This was evident from the micro-coagulam formation and        the appearance of a residual fine material in the storage        vessel.

Example 13—Microscopic Data

Two films were produced from the latex compositions set out in thefollowing table. It is noted that the composition of 13-2 differs fromthat of 13-1 in that it contains TiO₂ to provide whiteness andopaqueness. A cross-section was investigated through a scanning electronmicroscope and images taken. The elemental composition (C, Al, O, Ti)was analysed at a focussed spot using SEM. This revealed that aluminiumcould not be detected in the image for the film 13-1, even at highmagnification, due to the aluminium atoms being obscured by the carbonof the elastomeric film. This indicates that the aluminium has beendeeply and completely incorporated into the film structure, at theintra-particle and inter-particle level.

Composition in phr Experiment No 13-1 13-2 Polymer 100 100 KOH 1.7 1.7SDBS-Surfactant 0.3 0.3 SLES-Surfactant 0.3 0.3 TiO2 0 3 Sodiumaluminate 0.15 0.15 NaOH 0.15 0.15 KOH (for crosslinker solution) 0.150.15 Glycerin 0.15 0.15

FIGS. 1-5 contain the images of the two films produced by a scanningelectron microscope.

FIGS. 1, 2 and 5 relate to the composition of Example 13-2 (previouslynumbered Example 9-2). In FIGS. 1 and 2, one peak possibly omitted wasat 2.051 keV. FIG. 1 shows a cluster of white particles, being TiO₂particles, indicative of a non-solubilised metal oxide component (apigment, rather than a cross-linking agent). The magnification in FIG. 1is 15,000× magnification, with the scale bar indicated representing adistance of about 200 nm. FIG. 2 is of the same image at a differentdegree of magnification (5,000×, with the scale bar representing 1 μm).FIG. 5 is the same image but focusing on a different section, showingfurther clusters of white TiO₂ particles. The magnification is 25,000×,and the scale bar represents 300 nm.

The elements analysed in the SEM image for the Example 13-2 product wereC, O, Al and Ti. In processing, all elements indicated were analysed(normalised). There was one iteration. These are based on standards foreach element which were as follows:

-   -   Carbon: CaCO₃    -   Oxygen: SiO₂    -   Aluminium: Al₂O₃    -   Titanium: Ti

The % amounts of each detected for the composition of Example 13-2,based on atomic amounts, were as follows:

Element Weight % Atomic % C K 34.05 50.59 O K 33.05 36.86 Al K 1.01 0.67Ti K 31.88 11.88 Totals 100.00

In the results in the table above, the SEM was focussed on a very smallarea, roughly 0.2 micron×0.2 micron width, where a cluster ofundispersed TiO₂ was found. The higher than expected Aluminium amountwas due to the adherence of Aluminium to the TiO₂ cluster. In normalcured elastomeric areas, the aluminium could not be detected.

FIGS. 3 and 4 relate to the product of Example 13-1. In FIGS. 3 and 4,no peaks were omitted. FIG. 3 shows a uniform surface with proper andeven distribution of the aluminium inside the elastomeric matrix. Thevisible dents are surface undulations. The magnification in FIG. 3 is25,000×, with the scale bar indicated representing a distance of about200 nm. FIG. 4 is of the same image at a different degree ofmagnification (15,000× magnification, with the scale bar representing200 nm).

The elements analysed were C, O, Al and Ti. In processing, all elementsindicated were analysed (normalised) and those detected are indicated inthe table below. There were 2 iterations. The elemental analysis wasbased on the following standards:

-   -   Carbon: CaCO₃    -   Oxygen: SiO₂

The % amounts of each detected for the composition of Example 13-1,based on atomic amounts, were as follows:

Element Weight % Atomic % C K 88.71 91.28 O K 11.29 8.72 Totals 100.00

Items:

1. A synthetic elastomeric article comprising the cured product of asynthetic latex composition, the synthetic latex composition comprisinga synthetic carboxylated polymer and a cross-linking composition, thecross-linking composition comprising an aqueous solution of a negativelycharged multivalent metal complex ion having a pH of at least 9.0.

1(i) A synthetic elastomeric article comprising the cured product of asynthetic latex composition, the synthetic latex composition comprisinga synthetic carboxylated polymer and a cross-linking composition, thecross-linking composition comprising an aqueous solution of a multimetaloxide of the multivalent metal, a hydroxide of the multivalent metal, ora salt of the multivalent metal producing an aqueous solution ofnegatively charged multivalent metal complex ion having a pH of at least9.0, in which the amount of the multimetal oxide of the multivalentmetal, the hydroxide of the multivalent metal, or the salt of themultivalent metal is less than 0.3 phr.

1(ii). A synthetic elastomeric article comprising the cured product of asynthetic latex composition, the synthetic latex composition comprisinga synthetic carboxylated polymer and a cross-linking composition, thecross-linking composition comprising an aqueous solution of a negativelycharged multivalent metal complex ion having a pH of at least 9.0, thesynthetic latex composition further comprising a second cross-linkingagent comprising either (a) sulphur and a sulphur donor, (b) amultivalent metal oxide or ionic cross-linking agent, (c) sulphur, asulphur donor and an ionic cross-linking agent, or (d) sulphur donor.

1(iii). A synthetic elastomeric article comprising the cured product ofa synthetic latex composition, the synthetic latex compositioncomprising a synthetic carboxylated polymer and a cross-linkingcomposition, the cross-linking composition comprising an aqueoussolution of a negatively charged multivalent metal complex ion having apH of at least 9.0, wherein the article is a glove having an averagethickness of 0.2 mm or less and a modulus at 500% of less than 6.5 MPa.

1(iv). A synthetic elastomeric article comprising the cured product of asynthetic latex composition, the synthetic latex composition comprisinga synthetic carboxylated polymer and a cross-linking composition, thecross-linking composition comprising an aqueous solution of a negativelycharged multivalent metal complex ion having a pH of at least 9.0, thecross-linking composition further comprising a mechanical stabiliser orsurfactant, or a combination thereof.

1(v). A synthetic elastomeric article comprising the cured product of asynthetic latex composition, the synthetic latex composition comprisinga synthetic carboxylated polymer and a cross-linking composition, thecross-linking composition comprising an aqueous solution of a negativelycharged multivalent metal complex ion having a pH of at least 9.0,wherein said cross-linking composition comprises a solution of amultimetal oxide of the multivalent metal, a solution of a hydroxide ofthe multivalent metal, or a solution of a salt of the multivalent metal,which is other than a solution of sodium aluminate.

1(vi). A synthetic elastomeric article comprising the cured product of asynthetic latex composition, the synthetic latex composition comprisinga synthetic carboxylated polymer and a cross-linking composition, thecross-linking composition comprising an aqueous solution of a negativelycharged multivalent metal complex ion having a pH of at least 9.0,wherein at least one of the following applies:

-   -   i. the cross-linking composition comprises an aqueous solution        of a multimetal oxide of the multivalent metal, a hydroxide of        the multivalent metal, or a salt of the multivalent metal, such        as sodium aluminate, in an amount of less than 0.3 phr of the        multimetal oxide of the multivalent metal, the hydroxide of the        multivalent metal, or the salt of the multivalent metal;    -   ii. the synthetic latex composition comprises a second        cross-linking agent comprising sulphur and a sulphur donor;    -   iii. the synthetic latex composition comprises a second        cross-linking agent comprising a multivalent metal oxide or        ionic cross-linking agent;    -   iv. the synthetic latex composition comprises a second        cross-linking agent comprising sulphur, a sulphur donor and an        ionic cross-linking agent;    -   v. the synthetic latex composition comprises a second        cross-linking agent comprising a sulphur donor;    -   vi. the cross-linking composition comprises a mechanical        stabiliser and/or surfactant;    -   vii. the cross-linking composition comprises a solution of a        multimetal oxide of the multivalent metal, a solution of a        hydroxide of the multivalent metal, or a solution of a salt of        the multivalent metal, which is other than a solution of sodium        aluminate;    -   viii. the article is a glove having an average thickness of 0.2        mm or less and a modulus at 500% of less than 6.5 MPa.

2. The synthetic elastomeric article of any of items 1 to 1(vi), whereinthe synthetic carboxylated polymer comprises synthetic carboxylatedpolymer particles, and in the cured product the synthetic carboxylatedpolymer particles are bonded to each other through intra-polymerparticle multivalent metal cross-links and inter-polymer particlemultivalent metal cross-links, in which the intra-polymer particle andinter-polymer particle multivalent metal cross-links are uniformlydistributed throughout the cured product.

3. The synthetic elastomeric article of item 1 or item 2, having amodulus at 500% of less than 7 MPa.

4. The synthetic elastomeric article of any one of items 1 to 3, havingan elongation at break of at least 700%.

5. The synthetic elastomeric article of item 1 or item 2, having amodulus at 500% of less than 7 MPa and an elongation at break of atleast 700%.

6. The synthetic elastomeric article of any one of the preceding items,wherein the article is in the form of a film.

7. The synthetic elastomeric article of any one of the preceding items,wherein the article is a glove.

8. The synthetic elastomeric article of any one of the preceding items,wherein the multivalent metal of the negatively-charged multivalentmetal complex ion is an amphoteric metal.

9. The synthetic elastomeric article of any one of the preceding items,wherein the multivalent metal of the negatively-charged multivalentmetal complex ion is selected from the group consisting of aluminium,beryllium, chromium, iron, cobalt, copper, zinc, lead, tin and bismuth.

10. The synthetic elastomeric article of any one of the precedingclaims, wherein the multivalent metal of the negatively-chargedmultivalent metal complex ion is aluminium.

11. The synthetic elastomeric article of any one of the preceding items,wherein the cross-linking composition comprises a solution in water at apH of at least of 9.0 of a multimetal oxide of the multivalent metal, ahydroxide of the multivalent metal or a salt of the multivalent metal.

12. The synthetic elastomeric article of item 11, wherein thecross-linking composition comprises a solution of the multimetal oxideof the multivalent metal or a solution of the multivalent metalhydroxide.

13. The synthetic elastomeric article of any one of the preceding items,wherein the cross-linking composition comprises a solution of sodiumaluminate producing negatively-charged aluminium complex ions.

14. The synthetic elastomeric article of any one of the preceding items,wherein the cross-linking composition comprises alkali.

15. The synthetic elastomeric article of item 14, wherein thecross-linking composition comprises sodium hydroxide, potassiumhydroxide or ammonium hydroxide.

16. The synthetic elastomeric article of any one of the preceding items,wherein the cross-linking composition comprises a stabiliser formaintaining the negatively-charged multivalent metal complex ions insolution.

17. The synthetic elastomeric article of item 16, wherein the stabiliseris selected from the group consisting of glycerine, maltodextrin,polysaccharide, polyglycerol and mixtures thereof.

18. The synthetic elastomeric article of any one of the preceding items,wherein the amount of multivalent metal in the synthetic latexcomposition is 0.01-5 phr.

19. The synthetic elastomeric article of any one of the preceding items,wherein the amount of multivalent metal in the synthetic latexcomposition is 0.01-0.5 phr.

20. The synthetic elastomeric article of any one of the preceding items,wherein the synthetic carboxylated polymer is selected from the groupconsisting of carboxylated nitrile butadiene rubber, carboxylatedstyrene butadiene rubber, carboxylated butyl rubber, carboxylatedacrylic butadiene rubber, carboxylated polyisoprene, carboxylatedpolychloroprene, and mixtures or copolymers thereof.

21. The synthetic elastomeric article of any one of the preceding items,wherein the synthetic carboxylated polymer is carboxylated acrylonitrilebutadiene rubber.

22. The synthetic elastomeric article of any one of the preceding items,comprising a second cross-linking agent.

23. The synthetic elastomeric article of item 22, wherein the secondcross-linking agent is incorporated into the latex composition in solidform.

24. The synthetic elastomeric article of item 22 or item 23, wherein thesecond cross-linking agent comprises sulphur, a sulphur donor, or acombination thereof.

25. The synthetic elastomeric article of item 24, wherein sulphur isincluded in the latex composition in an amount of 0.1-5.5 phr.

26. The synthetic elastomeric article of item 24 or item 25, wherein asulphur donor is included in the latex composition in an amount of0.1-4.0 phr.

27. The synthetic elastomeric article of any one of items 22 to items26, wherein the second cross-linking agent comprises an organiccross-linking agent.

28. The synthetic elastomeric article of item 27, wherein the organiccross-linking agent is present in the latex composition in an amount of0.1-4.0 phr.

29. The synthetic elastomeric article of any one of items 22 to 28,wherein the second cross-linking agent comprises an ionic cross-linkingagent selected from the group consisting of zinc oxide, magnesium oxideand combinations thereof.

30. The synthetic elastomeric article of item 29, wherein the amount ofionic cross-linking agent in the latex composition is 0.1-4.0 phr.

31. An elastomeric article-forming composition comprising:

-   -   a synthetic carboxylated polymer, and    -   a cross-linking composition, the cross-linking composition        comprising an aqueous solution of a negatively-charged        multivalent metal complex ion having a pH of at least 9.0.

31(i) An elastomeric article-forming composition comprising:

-   -   a synthetic carboxylated polymer, and    -   a cross-linking composition, the cross-linking composition        comprising an aqueous solution of a multimetal oxide of the        multivalent metal, a hydroxide of the multivalent metal, or a        salt of the multivalent metal, producing a negatively-charged        multivalent metal complex ion, and having a pH of at least 9.0,        in which the amount of the multimetal oxide of the multivalent        metal, the hydroxide of the multivalent metal, or the salt of        the multivalent metal is less than 0.3 phr.

31(ii). An elastomeric article-forming composition comprising:

-   -   a synthetic carboxylated polymer,    -   a cross-linking composition, the cross-linking composition        comprising an aqueous solution of a negatively-charged        multivalent metal complex ion having a pH of at least 9.0, and    -   a second cross-linking agent comprising either (a) sulphur and a        sulphur donor, (b) a multivalent metal oxide or ionic        cross-linking agent, (c) sulphur, a sulphur donor and an ionic        cross-linking agent, or (d) sulphur donor.

31(iii). An elastomeric article-forming composition comprising:

-   -   a synthetic carboxylated polymer, and    -   a cross-linking composition, the cross-linking composition        comprising an aqueous solution of a negatively-charged        multivalent metal complex ion having a pH of at least 9.0,        wherein the composition can form gloves having an average        thickness of 0.2 mm or less and a modulus at 500% of less than        6.5 MPa.

31(iv). An elastomeric article-forming composition comprising:

-   -   a synthetic carboxylated polymer, and    -   a cross-linking composition, the cross-linking composition        comprising an aqueous solution of a negatively-charged        multivalent metal complex ion having a pH of at least 9.0, and a        mechanical stabiliser and/or surfactant.

31(v). An elastomeric article-forming composition comprising:

-   -   a synthetic carboxylated polymer, and    -   a cross-linking composition, the cross-linking composition        comprising an aqueous solution of a multimetal oxide of the        multivalent metal, a solution of a hydroxide of the multivalent        metal or a solution of a salt of the multivalent metal, which is        other than a solution of sodium aluminate, producing a        negatively-charged multivalent metal complex ion having a pH of        at least 9.0.

31(vi). An elastomeric article-forming composition comprising:

-   -   a synthetic carboxylated polymer, and    -   a cross-linking composition, the cross-linking composition        comprising an aqueous solution of a negatively-charged        multivalent metal complex ion having a pH of at least 9.0,        wherein at least one of the following applies:    -   i. the cross-linking composition comprises an aqueous solution        of a multimetal oxide of the multivalent metal, a hydroxide of        the multivalent metal, or a salt of the multivalent metal, such        as sodium aluminate, in an amount relative to the synthetic        carboxylated polymer to provide at least 0.01 phr and less than        0.3 phr of the multimetal oxide of the multivalent metal, the        hydroxide of the multivalent metal, or the salt of the        multivalent metal;    -   ii. the composition further comprises a second cross-linking        agent comprising sulphur and a sulphur donor;    -   iii. the composition further comprises a second cross-linking        agent comprising a multivalent metal oxide or ionic        cross-linking agent;    -   iv. the composition further comprises a second cross-linking        agent comprising sulphur, a sulphur donor and an ionic        cross-linking agent;    -   v. the composition further comprises a second cross-linking        agent comprising a sulphur donor;    -   vi. the cross-linking composition comprises a mechanical        stabiliser and/or surfactant;    -   vii. the cross-linking composition comprises a solution of a        multimetal oxide of the multivalent metal, a solution of a        hydroxide of the multivalent metal, or a solution of a salt of        the multivalent metal, which is other than a solution of sodium        aluminate;    -   viii. the composition can form gloves having an average        thickness of 0.2 mm or less and a modulus at 500% of less than        6.5 MPa.

32. The elastomeric article-forming composition of any one of items 31to 31(vi), wherein the multivalent metal of the negatively-chargedmultivalent metal complex ion is an amphoteric metal.

33. The elastomeric article-forming composition of any one of items 31to 32, wherein the multivalent metal of the negatively-chargedmultivalent metal complex ion is selected from the group consisting ofaluminium, beryllium, chromium, iron, cobalt, copper, zinc, lead, tinand bismuth.

34. The elastomeric article-forming composition of any one of items 31to 33, wherein the multivalent metal of the negatively-chargedmultivalent metal complex ion is aluminium.

35. The elastomeric article-forming composition of any one of items 31to 34, wherein the cross-linking composition comprises a solution inwater at a pH of at least of 9.0 of a multimetal oxide of themultivalent metal, a hydroxide of the multivalent metal or a salt of themultivalent metal.

36. The elastomeric article-forming composition of item 35, wherein thecross-linking composition comprises a solution of the multimetal oxideof the multivalent metal or a solution of the multivalent metalhydroxide.

37. The elastomeric article-forming composition of any one of items 31to 36, wherein the cross-linking composition comprises a solution ofsodium aluminate producing negatively-charged aluminium complex ions.

38. The elastomeric article-forming composition of any one of items 31to 37, wherein the cross-linking composition comprises alkali.

39. The elastomeric article-forming composition of item 38, wherein thecross-linking composition comprises sodium hydroxide, potassiumhydroxide or ammonium hydroxide.

40. The elastomeric article-forming composition of any one of items 31to 39, wherein the cross-linking composition comprises a stabiliser formaintaining the negatively-charged multivalent metal complex ions insolution.

41. The elastomeric article-forming composition of item 40, wherein thestabiliser is selected from the group consisting of glycerine,maltodextrin, polysaccharide, polyglycerol and mixtures thereof.

42. The elastomeric article-forming composition of any one of items 31to 41, wherein the amount of multivalent metal in the composition is0.01-5 phr.

43. The elastomeric article-forming composition of any one of items 31to 42, wherein the amount of multivalent metal in the composition is0.01-0.5 phr.

44. The elastomeric article-forming composition of any one of items 31to 43, wherein the synthetic carboxylated polymer is selected from thegroup consisting of carboxylated nitrile butadiene rubber, carboxylatedstyrene butadiene rubber, carboxylated butyl rubber, carboxylatedacrylic butadiene rubber, carboxylated polyisoprene, carboxylatedpolychloroprene, and mixtures or copolymers thereof.

45. The elastomeric article-forming composition of any one of items 31to 44, wherein the synthetic carboxylated polymer is carboxylatedacrylonitrile butadiene rubber.

46. The elastomeric article-forming composition of any one of items 31to 45, comprising a second cross-linking agent.

47. The elastomeric article-forming composition of item 46, wherein thesecond cross-linking agent is in solid form.

48. The elastomeric article-forming composition of item 46 or item 47,wherein the second cross-linking agent comprises sulphur, a sulphurdonor, or a combination thereof.

49. The elastomeric article-forming composition of item 48, whereinsulphur is included in the composition in an amount of 0.1-5.5 phr.

50. The elastomeric article-forming composition of item 48 or item 49,wherein a sulphur donor is included in the latex composition in anamount of 0.1-4.0 phr.

51. The elastomeric article-forming composition of any one of items 46to 50, wherein the second cross-linking agent comprises an organiccross-linking agent.

52. The elastomeric article-forming composition of item 51, wherein theorganic cross-linking agent is present in the composition in an amountof 0.1-4.0 phr.

53. The elastomeric article-forming composition of any one of items 46to 52, wherein the second cross-linking agent comprises an ioniccross-linking agent selected from the group consisting of zinc oxide,magnesium oxide and combinations thereof.

54. The elastomeric article-forming composition of item 53, wherein theamount of ionic cross-linking agent in the composition is 0.1-4.0 phr.

55. A method of manufacturing a synthetic elastomeric articlecomprising:

-   -   adding a cross-linking composition comprising an aqueous        solution of a negatively-charged multivalent metal complex ion        having a pH of at least 9.0 to an aqueous suspension of a        synthetic carboxylated polymer having a pH of at least 9.0 to        produce a synthetic latex composition;    -   forming the synthetic latex composition into the shape of the        synthetic elastomeric article; and    -   curing the synthetic latex composition to form the synthetic        elastomeric article.

55(i). A method of manufacturing a synthetic elastomeric articlecomprising:

-   -   adding a cross-linking composition having a pH of at least 9.0        and comprising an aqueous solution of a multimetal oxide of the        multivalent metal, a hydroxide of the multivalent metal, or a        salt of the multivalent metal, which solution contains        negatively-charged multivalent metal complex ions, to an aqueous        suspension of a synthetic carboxylated polymer having a pH of at        least 9.0, in an amount to provide less than 0.3 phr of the        multimetal oxide of the multivalent metal, the hydroxide of the        multivalent metal, or the salt of the multivalent metal, to        produce a synthetic latex composition;    -   forming the synthetic latex composition into the shape of the        synthetic elastomeric article; and    -   curing the synthetic latex composition to form the synthetic        elastomeric article.

55(ii). A method of manufacturing a synthetic elastomeric articlecomprising:

-   -   adding (i) a cross-linking composition comprising an aqueous        solution of a negatively-charged multivalent metal complex ion        having a pH of at least 9.0 and (ii) a second cross-linking        agent comprising either: (a) sulphur and a sulphur donor, (b) a        multivalent metal oxide or ionic cross-linking agent, (c)        sulphur, a sulphur donor and an ionic cross-linking agent,        or (d) sulphur donor, to an aqueous suspension of a synthetic        carboxylated polymer having a pH of at least 9.0 to produce a        synthetic latex composition;    -   forming the synthetic latex composition into the shape of the        synthetic elastomeric article; and    -   curing the synthetic latex composition to form the synthetic        elastomeric article.

55(iii). A method of manufacturing a synthetic elastomeric articlecomprising:

-   -   adding a cross-linking composition comprising an aqueous        solution of a negatively-charged multivalent metal complex ion        having a pH of at least 9.0 to an aqueous suspension of a        synthetic carboxylated polymer having a pH of at least 9.0 to        produce a synthetic latex composition;    -   forming the synthetic latex composition into the shape of the        synthetic elastomeric article; and    -   curing the synthetic latex composition to form gloves having an        average thickness of 0.2 mm or less and a modulus at 500% of        less than 6.5 MPa.

55(iv). A method of manufacturing a synthetic elastomeric articlecomprising:

-   -   adding a cross-linking composition comprising an aqueous        solution of a negatively-charged multivalent metal complex ion        having a pH of at least 9.0 and a mechanical stabiliser and/or        surfactant, to an aqueous suspension of a synthetic carboxylated        polymer having a pH of at least 9.0 to produce a synthetic latex        composition;    -   forming the synthetic latex composition into the shape of the        synthetic elastomeric article; and    -   curing the synthetic latex composition to form the synthetic        elastomeric article,

55(v). A method of manufacturing a synthetic elastomeric articlecomprising:

-   -   adding a cross-linking composition having a pH of at least 9.0        and comprising an aqueous solution of multimetal oxide of the        multivalent metal, a solution of a hydroxide of the multivalent        metal, or a solution of a salt of the multivalent metal, which        is other than a solution of sodium aluminate, which solution        contains negatively-charged multivalent metal complex ions, to        an aqueous suspension of a synthetic carboxylated polymer having        a pH of at least 9.0, to produce a synthetic latex composition;    -   forming the synthetic latex composition into the shape of the        synthetic elastomeric article; and    -   curing the synthetic latex composition to form the synthetic        elastomeric article,

55(vi) A method of manufacturing a synthetic elastomeric articlecomprising:

-   -   adding a cross-linking composition comprising an aqueous        solution of a negatively-charged multivalent metal complex ion        having a pH of at least 9.0 to an aqueous suspension of a        synthetic carboxylated polymer having a pH of at least 9.0 to        produce a synthetic latex composition;    -   forming the synthetic latex composition into the shape of the        synthetic elastomeric article; and    -   curing the synthetic latex composition to form the synthetic        elastomeric article,        wherein at least one of the following applies:    -   i. the cross-linking composition comprises an aqueous solution        of a multimetal oxide of the multivalent metal, a hydroxide of        the multivalent metal, or a salt of the multivalent metal, and        is added in an amount to provide less than 0.3 phr of the        multimetal oxide of the multivalent metal, the hydroxide of the        multivalent metal, or the salt of the multivalent metal;    -   ii. a second cross-linking agent comprising sulphur and a        sulphur donor is added to the synthetic carboxylated polymer;    -   iii. a second cross-linking agent comprising a multivalent metal        oxide or ionic cross-linking agent is added to the synthetic        carboxylated polymer;    -   iv. a second cross-linking agent comprising sulphur, a sulphur        donor and an ionic cross-linking agent is added to the synthetic        carboxylated polymer;    -   v. a second cross-linking agent comprising a sulphur donor is        added to the synthetic carboxylated polymer;    -   vi. the cross-linking composition comprises a mechanical        stabiliser and/or surfactant;    -   vii. the cross-linking composition comprises a solution of a        multimetal oxide of the multivalent metal, a solution of a        hydroxide of the multivalent metal, or a solution of a salt of        the multivalent metal, which is other than a solution of sodium        aluminate;    -   viii. the synthetic latex composition is cured to form gloves        having an average thickness of 0.2 mm or less and a modulus at        500% of less than 6.5 MPa.

56. The method of any one of items 55 to 55(vi), wherein thecross-linking composition is added sufficiently slowly to the aqueoussuspension of synthetic carboxylated polymer to avoid localisedcoagulation due to pH shock.

57. The method of item 56, wherein the pH of the cross-linkingcomposition is within 1.0 units of the pH of the aqueous suspension ofthe synthetic carboxylated polymer.

58. The method of any one of items 55 to 57, comprising adding alkali tothe aqueous suspension of the synthetic carboxylated polymer prior tothe addition of the cross-linking composition to raise the pH of theaqueous suspension to at least 9.0.

59. The method of any one of items 55 to 58, comprising adding thecross-linking composition to the aqueous suspension of the syntheticcarboxylated polymer when the concentration of multivalent metal ions inthe cross-linking composition is between about 1% and 10% by weight ofthe cross-linking composition.

60. The method of any one of items 55 to 59, comprising adding thecross-linking composition in an amount of between about 1 and 20 partsper 100 parts by volume of the aqueous suspension of the syntheticcarboxylated polymer.

61. The method of any one of items 55 to 60, comprising addingsurfactant to the aqueous suspension of synthetic carboxylated polymertogether with the cross-linking composition.

62. The method of any one of items 55 to 61, wherein the step of formingthe latex composition into the shape of the synthetic elastomericarticle comprises a dipping a former into the latex composition.

63. The method of item 62, wherein the former is a glove-shaped former,and the method is for the manufacture of a glove.

64. The method of item 62 or item 63, comprising dipping the former intoa coagulant composition prior to the step of dipping the former into thelatex composition.

65. The method of any one of items 55 to 64, wherein the multivalentmetal of the negatively-charged multivalent metal complex ion is anamphoteric metal.

66. The method of any one of items 55 to 65, wherein the multivalentmetal of the negatively-charged multivalent metal complex ion isaluminium.

67. The method of any one of items 55 to 66, comprising adding thecross-linking composition to the aqueous suspension of the syntheticcarboxylated polymer in an amount to provide 0.01-5 phr of multivalentmetal in the latex composition.

68. The method composition of any one of items 55 to 67, comprisingadding the cross-linking composition to the aqueous suspension of thesynthetic carboxylated polymer in an amount to provide 0.01-0.5 phr ofmultivalent metal in the latex composition.

69. The method of any one of items 55 to 68, comprising forming thecross-linking composition by solubilising a multimetal oxide of themultivalent metal, a hydroxide of the multivalent metal or a salt of themultivalent metal in water, and controlling the pH to be at least 9.0.

70. The method of item 69, comprising forming the cross-linkingcomposition by solubilising sodium aluminate in water with heating.

71. The method of item 69 or item 70, wherein the step of forming thecross-linking composition comprises adding an alkali to raise the pH ofthe cross-linking composition to at least 9.0.

72. The method of any one of items 69 to 71, comprising adding astabiliser to the cross-linking composition to maintain the multivalentmetal complex ions in solution, to form a stabilised cross-linkingcomposition, prior to addition of the cross-linking composition to theaqueous suspension of synthetic carboxylated polymer.

73. The method of item 72, wherein the stabiliser is selected from thegroup consisting of glycerin, maltodextrin, polysaccharide, polyglyceroland mixtures thereof.

74. The method of any one of items 69 to 73, comprising a step ofdiluting the cross-linking composition to obtain a multivalent metal ionconcentration of between 1-10% by weight of the cross-linkingcomposition, prior to the addition of the cross-linking composition tothe aqueous suspension of a synthetic carboxylated polymer.

75. The method of any one of items 55 to 74, wherein the syntheticcarboxylated polymer comprises synthetic carboxylated polymer particles,and the curing step results in the synthetic carboxylated polymerparticles being bonded to each other through intra-polymer particlemultivalent metal cross-links and inter-polymer particle multivalentmetal cross-links, in which the intra-polymer particle and inter-polymerparticle multivalent metal cross-links are uniformly distributedthroughout the cured product.

76. The method of any one of items 55 to 75, wherein the syntheticcarboxylated polymer is selected from the group consisting ofcarboxylated nitrile butadiene rubber, carboxylated styrene butadienerubber, carboxylated butyl rubber, carboxylated acrylic butadienerubber, carboxylated polyisoprene, carboxylated polychloroprene, andmixtures or copolymers thereof.

77. The method of any one of items 55 to 44, wherein the syntheticcarboxylated polymer is carboxylated acrylonitrile butadiene rubber.

78. The method of any one of items 55 to 77, comprising adding to thelatex composition particulate components selected from the groupconsisting of second cross-linking agents, plasticizers, anti-ozonants,stabilisers such as pH stabilisers, emulsifiers, antioxidants,vulcanising agents, pigments, fillers, colourising agents andsensitisers prior to forming the latex composition into the shape of thesynthetic elastomeric article.

79. The method of item 78, wherein the particulate components comprise asecond cross-linking agent.

80. The method of item 79, wherein the second cross-linking agentcomprises sulphur, a sulphur donor, or a combination thereof.

81. The method of item 80, wherein sulphur is added into the latexcomposition in an amount of 0.1-5.5 phr.

82. The method of item 80 or item 81, wherein a sulphur donor is addedinto the latex composition in an amount of 0.1-4.0 phr.

83. The method of any one of items 79 to 82, wherein the secondcross-linking agent comprises an organic cross-linking agent.

84. The method of item 83, wherein the organic cross-linking agent isadded to the latex composition in an amount of 0.1-4.0 phr.

85. The method of any one of items 79 to 84, wherein the secondcross-linking agent comprises an ionic cross-linking agent selected fromthe group consisting of zinc oxide, magnesium oxide and combinationsthereof.

86. The method of item 53, wherein the ionic cross-linking agent isadded into the latex composition in an amount of 0.1-4.0 phr.

87. An elastomeric article produced from the elastomeric article-formingcomposition of any one of items 31 to 54 or by the method of any one ofitems 55 to 86.

88. Elastomeric gloves produced from the elastomeric film-formingcomposition of any one of items 31 to 54 or by the method of any one ofitems 55 to 86.

89. A synthetic elastomeric article comprising cured syntheticcarboxylated polymer particles bonded to each other throughintra-polymer particle multivalent metal cross-links and inter-polymerparticle multivalent metal cross-links, in which the intra-polymerparticle and inter-polymer particle multivalent metal cross-links areuniformly distributed throughout the cured product.

90. The synthetic elastomeric article of item 89, and comprising thefeatures of any one of items 1 to 30.

1. A synthetic elastomeric article comprising the cured product of asynthetic latex composition, the synthetic latex composition comprisinga synthetic carboxylated polymer and a cross-linking composition, thecross-linking composition comprising an aqueous solution of a negativelycharged multivalent metal complex ion having a pH of at least 9.0, thesynthetic latex composition further comprising a second cross-linkingagent comprising either (a) sulphur and a sulphur donor, (b) amultivalent metal oxide or ionic cross-linking agent, (c) sulphur, asulphur donor and an ionic cross-linking agent, or (d) sulphur donor. 2.The synthetic elastomeric article of claim 1, wherein the syntheticcarboxylated polymer comprises synthetic carboxylated polymer particles,and in the cured product the synthetic carboxylated polymer particlesare bonded to each other through intra-polymer particle multivalentmetal cross-links and inter-polymer particle multivalent metalcross-links, in which the intra-polymer particle and inter-polymerparticle multivalent metal cross-links are uniformly distributedthroughout the cured product.
 3. The synthetic elastomeric article ofclaim 1, having a modulus at 500% of less than 6.5 MPa.
 4. The syntheticelastomeric article of claim 1, wherein the article is a glove.
 5. Thesynthetic elastomeric article of claim 1, wherein the multivalent metalof the negatively-charged multivalent metal complex ion is aluminium. 6.The synthetic elastomeric article of claim 1, wherein the cross-linkingcomposition comprises a solution of sodium aluminate producingnegatively-charged aluminium complex ions.
 7. The synthetic elastomericarticle of claim 1, wherein the amount of multivalent metal in thesynthetic latex composition is 0.01-0.5 phr.
 8. The syntheticelastomeric article of claim 1, wherein the second cross-linking agentcomprises (a) sulphur and a sulphur donor, and is free of solidmultivalent metal oxide.
 9. The synthetic elastomeric article of claim1, wherein the second cross-linking agent comprises (b) a multivalentmetal oxide or ionic cross-linking agent, and is free of sulphur andsulphur donors.
 10. The synthetic elastomeric article of claim 1,wherein the second cross-linking agent comprises (d) a sulphur donor,and is free of sulphur and solid multivalent metal oxide.
 11. Thesynthetic elastomeric article of claim 1, wherein the amount of eachsecond cross-linking agent is not more than 1.0 phr.
 12. The syntheticelastomeric article of claim 1, wherein the total amount of all secondcross-linking agents is not more than 1.0 phr.
 13. An elastomericarticle-forming composition comprising: a synthetic carboxylatedpolymer, a cross-linking composition, the cross-linking compositioncomprising an aqueous solution of a negatively-charged multivalent metalcomplex ion having a pH of at least 9.0, and a second cross-linkingagent comprising either (a) sulphur and a sulphur donor, (b) amultivalent metal oxide or ionic cross-linking agent, (c) sulphur, asulphur donor and an ionic cross-linking agent, or (d) sulphur donor.14. A method of manufacturing a synthetic elastomeric articlecomprising: adding (i) a cross-linking composition comprising an aqueoussolution of a negatively-charged multivalent metal complex ion having apH of at least 9.0 and (ii) a second cross-linking agent comprisingeither: (a) sulphur and a sulphur donor, (b) a multivalent metal oxideor ionic cross-linking agent, (c) sulphur, a sulphur donor and an ioniccross-linking agent, or (d) sulphur donor, to an aqueous suspension of asynthetic carboxylated polymer having a pH of at least 9.0 to produce asynthetic latex composition; forming the synthetic latex compositioninto the shape of the synthetic elastomeric article; and curing thesynthetic latex composition to form the synthetic elastomeric article.15. The method of claim 14, wherein the cross-linking composition isadded sufficiently slowly to the aqueous suspension of syntheticcarboxylated polymer to avoid localised coagulation due to pH shock. 16.The method of claim 14, wherein the step of forming the latexcomposition into the shape of the synthetic elastomeric articlecomprises a dipping a glove-shaped former into the latex composition,and the method is for the manufacture of a glove.
 17. The method ofclaim 14, comprising forming the cross-linking composition bysolubilising sodium aluminate in water with heating.
 18. The method ofclaim 14, comprising adding the cross-linking composition to the aqueoussuspension of the synthetic carboxylated polymer in an amount to provide0.01-0.5 phr of multivalent metal in the latex composition.
 19. Themethod of claim 14, wherein the amount of each second cross-linkingagent that is added is not more than 1.0 phr.
 20. The method of claim14, wherein the total amount of all second cross-linking agents added isnot more than 1.0 phr.